Premature and Congenitally Diseased Infants

by Julius H. Hess, M.D.

Chapter III
Physiology

The appearance and characteristics of the healthy premature child vary with the fetal age at the time of birth. With a lengthening of the period of gestation, the` distinctive characteristics of the fetus become less and less marked until it becomes impossible to differentiate the slightly premature from the full-term infant. All the distinguishing features of the premature may also be, found in the congenitally diseased full-term infants, and as there may be all degrees of prematurity, so we also find all stages of development between the extremes of functional and anatomical inferiority on the one hand and the normal constitution on the other. Both the premature and the debilitated infant may exhibit the following features in varying degrees.

The body is usually small and puny, though in some instances the infant may be of a considerable size, yet with a very imperfect development of its internal organs.

The weight is low, varying from amounts approximating 700 gm. (1 1/2 lbs.) to 2500. gm. (5 1/2 lbs.) in the viable. The latter figure may be exceeded in infants nearing maturity, and by some of the full-term weaklings, but will serve as a fair maximum.

The skin is soft and usually of a vivid red color. The epidermis is thin and the blood vessels are easily seen.

The skin frequently hangs in folds. The adipose tissue is scant, the features are angular and the face looks old.

Lanugo is plentiful, especially upon the extensor surfaces of the extremities.

The skull is round or ovoid in contradistinction to the usually markedly dolichocephalic skull of the full-term new-born. The fontanelles are large and the sutures prominent.

The nose, exhibits many small comedones. The ears are soft and small and hug the skull.

The nails have scarcely reached the ends of the fingers even in the larger infants, while in the smaller they may be very poorly developed. The cry is feeble, monotonous and whining.

The infant lies in a deep sleep, and must be aroused for its feedings. Efforts at suction are weak or absent. All movements are slow, functions are sluggish and the child shows a remarkable degree of muscular inertia.

The temperature has a very decided tendency to remain below-normal and is inclined to be irregular in character.

The urine is usually scanty.

The bowels are sluggish and constipation is the rule. Early and intense jaundice is common.

These are the principal findings which are to be seen on superficial examination. A more critical review of these various characteristics follows. It must be remembered that any of these symptoms may vary in different individuals of the same age, depending upon the cause of prematurity, and upon the condition of health present in both the mother and the child. With increasing age, the characteristics become less marked, until the picture eventually merges into that of the full-term infant.

The determination of the exact age of the infant prematurely born is a matter of considerable difficulty. The information furnished by the mother as to the time of her last menstrual period, or as to the time when life was first felt, gives an entirely insufficient approximation of the probable date of confinement, and errors of a month or even more are not rare. In institutions for foundlings all data is, as a rule, absent, and other methods for determining the infant's fetal age must be relied upon. The weight of the infant is of uncertain value also, as an infant of 1500 gm. weight may be the product of a pregnancy of seven months in a healthy woman, while one of the same or less weight may be the eighth-month offspring of an albuminuric or syphilitic mother. The body measurements also vary materially with the individual. The degree of development of the osseous system is of great value in determining the anatomical development, and indirectly the condition of the bones acts as a guide to physiological development, even though they do not give absolute data as to age. Body measurements and osseous development are fully discussed later under their respective headings.

More important than a determination of the approximate term of pregnancy or a consideration of the size of the infant, at least in those infants born but a few weeks before the natural termination of the period, is a history of syphilis, tuberculosis, traumata, or other causes, operating in the mother and responsible for the early emptying of the uterus.

His gives the following description of the developmental features of the fetus at varying ages:

Fifth Lunar Month (112 to 140 days).-Head about the size of hen's egg; the skin is red and shows some fat deposit. The scalp shows indications of hair, the body is covered with lanugo, the nails can be distinguished, the eyelids remain closed. The fetus rarely lives over five to ten minutes, making feeble attempts at respiration. The heart-beats may be strong.

Sixth Lunar Month (140 to 168 days).-The body shows increased fat deposits, though still lean, the skin being wrinkled. The eyelids are separated and eyebrows and lashes may be seen. The infant may live for several hours. The respiratory and digestive organs are underdeveloped, respirations being superficial and digestion practically impossible.

Seventh Lunar Month (168 to 196 days).-The infant has an aged appearance but the wrinkles are filling out. The eyes are open. The cry is a weak whine or grunt. Few of these infants born during the twenty-fifth and twenty-sixth weeks survive, and when they do are usually hydrocephalic, paralytic and dwarfed. Those of the twenty-seventh and twenty-eighth weeks are far more promising.

Eighth Lunar Month (196 to 224 days).-The infant is beginning to fill out, many of the wrinkles having disappeared. The bones of the head are soft and flexible. Ossification begins in the lower epiphysis of the femur. The testicles are often in the scrotum. The cry is stronger, though it may still be very weak. Under proper conditions many of these infants survive.

Ninth Lunar Month (224 to 252 days). -Panniculus adiposus develops. The wrinkles smooth out and the limbs become rounded. The lanugo begins to disappear, and the nails are at the tips of the fingers. Respiratory, circulatory and digestive organs are capable of carrying on the. body functions.

Tenth Lunar Month (252 to 280 days).-The general body functions improve during this month and at the end of this period development is complete.

Infants born at full-term weigh on the average from 3000 to 3500 gm. The dividing line between the premature and full-term infant has been generally placed at 2500 gm. If under that figure they may be considered below par as far as concerns the strength and ability to overcome the forces which assail them on every hand. The weight of the premature varies even within greater limits than that of the full-term infant, and as one may see a child below 2500 gm, so also there are prematures with a weight above this limit.

The weight depends upon the cause of the premature birth and upon the age of the child. Those born of mothers afflicted with nephritis, tuberculosis, or other wasting diseases, and infants showing active syphilis, are usually considerably smaller than the same aged infants of healthy parents. Diseases and abnormal location of the placenta also restrict the growth of the fetus. The infant in placenta previa is often undersized, even when born at term. Multiparity may predispose to undersize.

His, in a comparison of the fetal weight and length with the age, made the following table:

The weight and length as compared to the fetal age is shown in the following table from Oberwarth, which gives the average length also:

These compare favorably with those given by Ahlfeld and Hecker.

Potel and Hahn's figures do not include the length.

The following small group taken from my cases give the age of the fetus as computed from. the date of the last menstruation. That this is an unreliable method may be recognized by noting the variation in figures in Cases 2, 3, 11, 13, 14 and 15. We therefore, place_. little reliance on the mother's estimate as to the date of conception.

In contrast with these measurements of the diameters of the head in prematures, the average measurements of the skull in a mature new born are noted as follows by Schauta.

1. Diameter suboccipito-bregmaticus (from the posterior edge of the great occipital foramen to the anterior angle of the great fontanelle), 9 cm.

2: Diameter fronto-occipitalis (from glabella to the occipital protuberance), 11 cm.

3. Diameter mento-occipitalis (from the point of the chin to the farthest point of the occiput), 13 cm.

4. Diameter verticalis (from the vertex to the base of the skull), 9.5 cm.

5. Diameter biparietalis (between the parietal tuberosities), 9 cm.

6. Diameter bitemporalis (between the farthest point of both coronary sutures), 8 cm.

Parents short in stature or small in build may have children who do not weigh over 2000 gm. or measure over 45 cm in length, and yet who are neither premature nor congenitally weak.

It does not do to estimate the vitality of these infants from a consideration of their birth weight. Many of them born at or near term have a normal weight, yet they do not survive. On the other hand, infants of considerably less weight may present evidence of great vitality, a lusty cry and take nourishment with avidity. According to our experience the condition of the turgor of the prematurely born infants is of much more importance than all these. Flabby prematures with a poor turgor and a poor tonus are usually not viable. Prematures with a good turgor and a good tonus even with a low weight commonly survive.

In addition to the variations in weight and length, the premature shows variations in other measurements.

Other Measurements of the Fetus.-Von Winckell regards the circumference of the head as of importance for the diagnosis of the age of the fetus and gives the following figures:

Reiche reports the following comparative body measurements:

These figures show a gradual and steady increase of the weight and the chest and head measurements, up to the time of maturity, when they should average 3200 gm in weight, 50.5 cm. in length, with a chest circumference of 32.9 to 33.8 cm. and a head circumference of 34.5 cm.

We see in the eighth to the tenth month an abrupt rise of the curve of chest circumference, the curve flattening somewhat soon after birth. This increase in the circumference of the chest in the last fetal months is considerably higher than that of a mature child during the first months after birth. In the latter the circumference of the chest increases from 32.5 to 37.2 at the end of the third month to 41 at the end of the sixth month, therefore in the first six months of life approximately about as much as in the last three fetal months.

In the curve of the growth of the skull the flattening appears even somewhat earlier. The ratio, however, between the growth of the skull in the last three fetal months and that in the first six months of life is the same as in the circumference of the chest. Also the circumference of the head grows absolutely and relatively considerably more in the last fetal months than in the first six months of life.

A proof for the correctness of these figures Reichel finds in the fact that the corresponding figures are considerably lower in children who die shortly after birth. They are premature weaklings whose intra-uterine development in spite of sufficient body weight did not attain such a degree that it might be completed in the extra-uterine life.

The corresponding figures are, as follows:

From these figures Reiche concludes that in premature weaklings the length of the body does not vary greatly from that of healthy children, but on the other hand the measurements of the circumference of the chest and of the circumference of the head are considerably smaller.

Ylppo recently studied the relation of the chest circumference to that of the head in prematures and full-term infants. He found that at birth the circumference of the bead is greater than that of the chest, and the greater the prematurity the more marked is the relative disproportion between the head and chest circumferences. These facts are borne out by his table:

In comparison with the preceding tables on prematures we note the conclusions drawn by von Reuss from his own work and the tabulations compiled by Weissenberg on the mature new-born infant.

The peculiarities of the proportions of the body characteristic of the full-term new born consist therefore of the following: Not only the sitting height, but also the height of the trunk proper is greater than the leg. The length of the trunk proper is greater than that of the arm. The arm is longer than the leg. The circumference of the head is usually greater than that of the chest. Occasionally the circumference of the head and chest are equal; in strongly built infants the circumference of the chest often exceeds that^-of the head. The body length approximates 47 to 54 cm. and errors in statements of length result because of the lack of consideration for the deformity of the skull and caput succedaneum (von Reuss).

Jaschkem in a recent study of the premature and debilitated child, came to the conclusion that there was less variability in certain relations between measurements of the body than was commonly thought. "In immature infants the fronto-occipital circumference of the head always is greater than the circumference of the shoulders (Frank and others), while in mature infants the opposite is true; also the proportion between the height of the head and the height of the body (Stratz) is disturbed since the height of the head is greater than one-fourth of the length of the body; this is due especially to relatively shorter legs" (Fig. 11).

Gundobin, studying the average weight of the inner organs of the mature new born in grams, noted the following:

In contrast with these figures, we may quote from the anatomical studies of Ylppo on premature infants.

Ylppo found several instances in which the large brain weight seemed to be out of proportion to the figures of other observers. His studies led him to believe that the brain of the premature (even the smallest) grows at the same rate as if the fetus were in utero and that it develops in extra-uterine life after certain given laws of Nature; thus, the small body weight having relatively little to do with the brain. In these cases of marked disproportion he found that when one compares the absolute age of the premature, from the time of conception, with that of a normal infant, it is seen that the brain weight of the two compare favorably. His conclusions were that the size of the brain has nothing to do with a hydrocephalic process, since it is not explained by an abnormal water content, and that the "megacephaly" of prematures is a physiological process.

Tonsils.-In prematures there appears at the site of the palatine tonsils only one or two small cavities. Only after four to five months does a glandular structure appear.

Thyroid Gland.-This is very small, but it has a very rich blood supply. In one case of a seven-months premature Ylppo observed an enlargement of the thyroid (1.5 gm.): weight of infant, 1270 gm.; length, 44 cm. Microscopically there were large quantities of colloid in the center of the follicles, but no hemorrhages or evidence of degenerative changes.

Thymus Gland.-In prematures of 1000 to 2000 gm it is between 1 and 3 gm., while in full-terms it may be as much as 20 gm. Gundobin estimated it in prematures of similar weight as on the average of 2.5 gm.

Heart.-The heart on the average is from 0.5 to 0.75 per cent of the body weight of prematures. In those from 900 to 1200 gm. Ylppo found that the weight ranged from 4.5 to 7 gm. In full-term infants and those with a longer intra-uterine growth (of the prematures), the relation between heart and body weight was found to remain about the same by Lomer, thus:

4000 gm infant – 27.6 gm heart = 0.7 per cent body weight

2-3000 gm infant – 20.7 gm heart

1-2000 gm infant – 11.4 gm heart

The ductus Botalli closes more slowly and later in prematures. On the average blood ceases to pass through after the end of the first or second week of life.

Liver.-The liver is the largest of the internal organs of the premature body. The smaller the premature, the greater is the relative size of the liver.

With the increase of body weight the liver weight slowly increases. The figures for the group of 1501 to 2000 gm. are too small, and are based only on four observations. The weight of the liver in prematures has to do with the richness of its blood supply.

Spleen.-The spleen, as the liver, is very rich in blood.

As with the liver, the spleen increases in size with increase in the body weight.

Kidneys.-The ratio between the weight of both kidneys and the body weight is greater in prematures than in full-terms and older infants:

Gundobin showed that in full-terms the percentage was 0.38 per cent.

Vierordt showed that in men between nineteen and twenty-five years of age the percentage was 0.48 per cent.

The embryonic features of the kidneys are very marked. The fetal markings disappear fairly rapidly. In one case of a sixth to seventh embryonic month premature of 1000 gm. birth weight, the fetal markings were gone after five to seven weeks of life (Ylppo).

During the intra-uterine life the child receives gratis the material necessary for its maintenance, for the development and regeneration of its cells. The maternal blood stream brings to the level of the placenta the oxygen and other substances needful for its nutrition, and the passing of these foods into the antenatal circulation requires no effort on the part of the fetus other than the cardiac contractions. From birth on, however, the child is an independent being and it must fight that it may live.

The upkeep of the somatic tissues is dependent upon the functions of the respiratory system and the digestive tract, and these activities require of the new-born infant an expenditure of energy of which it has had no previous experience. Before birth the energy resulting from intracellular combustion was transformed into that amount of heat necessary to the performance of the new cellulo-chemical reactions occurring in the fetus. After birth a much greater amount of energy is necessary because of the more extensive reactions taking place within the tissues and because of the appearance of motion. Increased metabolism is, therefore, necessary to the accomplishment of the digestive and respiratory functions and to enable the infant to fight against external physical agents, principally cold.

Cause and Nature of Hypothermia.-Heat regulation is one of the least developed functions of the premature infants, their body temperature showing marked fluctuation with a tendency to hypothermia. This is due to several factors:

1. Faulty Heat Regulation Due to Lack of Development on the Part of the Nervous System.-It is possible to imagine that in a premature infant where the development of the brain is still going on, and the separation into the white and gray matter has not been completed, that the nervous system is not sufficiently matured to function normally.

2. Loss of Heat Through Radiation.-The extent of the heat loss from the body of an animal by conduction, radiation, evaporation from the skin and the surface of the lungs is determined by the extent of the surface and by the thickness of the ill-conducting subcutaneous fatty layer; the heat loss, therefore, is in greater part proportional to the extent of the surface of the body. In a premature infant the body surface is relatively greater than in a full-weight new born, since the size of the body is absolutely smaller. Wrinkled skin and absence of the fat deposits in the skin are responsible for the greater loss of heat. It is these physical conditions which make it difficult for the premature to retain its own heat and predispose to the readiness with which the subnormal temperature can occur.

3. Insufficient Oxygen Combustion.-Due to a poorly developed respiratory center causing asphyxia.

Babak found that the lower the temperature in the respiratory chamber, the greater the consumption of oxygen, this corresponding to the irradiation of heat. The average values in one hour per gram of body weight amounted to:

From the results of this experiment it is clear that the infant's organism attempted to equalize the physical minus with the chemical plus. But in spite of the more intensive exchange of gases, the body temperature was sinking with a low external temperature and also when the infant was insufficiently covered. The increase in oxidation processes, therefore, was not sufficient to compensate for the increased heat radiation.

4. The Circulation.-The circulation is affected by its nervous mechanism and weak cardiac action is another important factor.

5. Insufficient Heat Production Due to Lack of Food or Improper Metabolism.-This cause of hypothermia is of minor importance in the premature infant which is fed a sufficient quantity of breast milk and shows ability to assimilate the same. As the sucking centers are too poorly developed to enable the infant to obtain sufficient nourishment, most of these infants cannot be trusted to their own resources in obtaining their food.

A careful consideration of all of the factors tending to hypothermia make it evident that we cannot depend on an equalization of the heat loss from the body surface by the internal production of heat, and therefore in order to maintain a uniform temperature it becomes necessary to assist the infant by giving it an artificial environment of good air sufficiently heated to maintain a normal body temperature.

Initial Weight Losses.-Loss of body weight during the first days of life occurs so constantly in full-term infants that moderate losses must be considered physiological. This is also true of premature infants although in most instances it is relatively greater. Premature infants lose relatively more and regain their birth weight more slowly, often requiring a month (De Lee) and also, as a general rule, the nearer the prematures are to full term, the lower is the relative loss of weight as expressed in percentages.

The average loss in weight in the premature and in other infants of relatively low birth weight during the first days of life is shown in the following table adapted from Reiche:

Gundobin's figures are considerably higher, as he came to the conclusion that the initial loss of weight in infants with a birth weight under 2000 gm amounted on the average to 148 gm.

The artificially-fed infants lose more weight than the breast fed, but no differences were noticeable between those infants nursing at the mother's breast and those fed by a wet-nurse (Reiche).

In children of multiparous women both the absolute and also the relative percentage value of the weight loss is smaller than in those of primiparous, which is undoubtedly due to better nursing conditions, milk appearing sooner in multiparae and being usually more abundant.

The loss of weight is also relatively larger the less the birth weight of the infant, as the following table taken from Pies will show:

Initial loss in weight rests upon the fact that the new-born infant gives off more than it takes in. The meconium is accountable for a considerable part of the loss. This averages in weight according to Camerer from 70 to 90 gm.; according to Hirsch from 150 to 200 gm. In addition to that, the urine voided before the child receives much fluid must be considered, though this is probably small. The water lost through the lungs and skin, the loss of the stump of the umbilical cord, and, in some cases, the vomiting of swallowed liquor amnii during the first twenty-four hours, are all factors in reducing the weight of the new born. Furthermore, it has been shown that there is a loss of the body tissues, of the fat, glycogen and albumin, as evidenced by the loose and wrinkled condition of the infant's skin, and lost turgor of the tissues in general. Landois found that the loss of weight in infants in whom the cord was tied late was 5.9 to 7.4 per cent less than those in whom the cord was tied and cut early.

Gundobin found that the lowest weight was usually reached sometimes between the fourth and sixth days in the full-term infant and that the birth weight was regained on the eleventh to the sixteenth day. Very frequently, however, and especially in weaklings and prematures, the birth weight was not regained as early as the sixteenth day, twenty or thirty days being required to make up the initial loss. The artificially-fed regained the loss later than the breast-fed infants.

Pfaundler, in his observations on 1000 new-born infants came to the conclusion that the physiological weight loss occurred in 42 per cent by the fourth day. The loss in the infants of from 1500 to 4000 gm. birth weight averaged 7.8 per cent of the latter, and was about the same for the. heavy as for the light, although it was relatively slightly greater in the former.

Ramsey and Alley noted in 300 cases that the average loss of weight continued for three days and was regained by the tenth day by only one-fourth of the infants.

Shick, believing that the initial loss of weight was avoidable, gave each infant 10 per cent of its body weight of breast milk the first twenty-four hours, increasing the amount until 15 per cent was given at the end of the third twenty-four hours. He employed the milk of mothers having infants less than a week old and was able to prevent the initial loss in all of his twelve cases.

The increase in weight of the prematures is noted in the table below in a group of the author's cases.

The growth of the premature infant has been well shown by the tables of Camerer, who figures out the daily average increase in ten infants who had a birth weight ranging from 1330 to 1970 gm.

Camerer compared the increase in weight in breast-fed and bottle-fed premature infants with an initial weight of from 1590 to 1740 gm.

Camerer's further figures also show that the artificially-fed full-term infant is much slower in its weight increase than the breast-fed child.

The average daily increase in weight of the premature of different periods as well as for the premature child is shown by Friedenthal:

The growth in length proceeds slowly from month to month, diminishing in rate (Friedenthal).

If these figures of Friedenthal's are plotted into a curve it is seen that the curve of the body weight and that of the body length run parallel up to the seventh or eighth month, at which time the length curve rises less abruptly than the weight curve.

Pfaundler found that the rate of growth in an infant born three months prematurely became the same as that. of a maturely born child when the premature had reached the age of three months. These figures apply, of course, to the healthy prematures only and not to those debilitated from disease or by unfavorable environment or food.

Reiche's investigations have shown that the growth of the prematures follows the same rules of growth that hold good for the corresponding months after impregnation. In healthy prematures there is no difference between the intra-uterine and extrauterine growth in the same months, so that the birth in itself causes no disturbance of growth provided that the infant has reached a certain stage of development, compatible with the exercise. of certain indispensable functions, e. g., respiration, circulation and digestion. This stage of development is seldom reached before the twenty-eighth week of life, when the infants are about 34 cm. long and weight approximately 1 kg. It has, therefore, been proposed to designate the age of the infant from the time of conception rather than from the time of birth. Serious chronic diseases of the mother (especially lues and tuberculosis) exert a growth-inhibiting influence upon the infant. Their progress is not governed by the same laws that hold good for healthy premature infants.

Reiche has also studied the relation between the growth in weight and the growth in length and has introduced the term length-weight coefficient, by which is understood the weight of a unit of length. The following table shows the birth-weight coefficient for different groups of prematurely born infants:

Langstein formulated the following law from the observations of Reiche and others: Both the growth in mass and the growth in length of these organisms in whom the transition from intra-uterine to extra-uterine life had to occur prematurely, proceeds according to the same laws that correspond to the period of time after impregnation.

The majority of multiple pregnancies terminate prematurely and therefore the percentage of twins among the prematurely born is considerably higher among mature children. By the development of more than one child in the mother's womb the growth may be impaired, and this consists, as a rule, in impairment of growth in mass, only in exceptional cases in impairment of growth in length.

But even in these prematurely born, twins have a tendency in their first months of life to make up this loss. The curves of growth of twins run, as long as no intercurrent diseases interfere, parallel to each other and also to the curve of those children in whom a larger difference in growth was present at birth. The proportions of growth between the circumference of the thorax and the circumference of the head are scarcely influenced by multiple pregnancy. In individual twins even these curves run parallel to each other.

Weight in Relation to the Body Surface. -Ssytcheff gives the following table comparing the surface area and the weight in the premature and in older children.

Thus it is seen that the larger the volume (weight) of the infant the smaller the surface area relative to that weight.

In estimating or comparing heat loss or other metabolic processes relating to or dependent upon surface area, it is evident that one should have an exact method of determining that area. Meeh, in 1879, was the first to construct a formula for this purpose, the basis for which was the observation of Molischott that the volume of bodies of similar composition and form varies in the ratio of the cube root of their weight and their surface areas in the ratio of the square root of their volume.

Recent investigations have given us two reliable formulae for the rapid estimation of the body surface of the infant, those of Dubois and DuBois and of Howland and Dana.

The formula of Dubois and DuBois, which is entirely independent of the body weight, predicates the division of the body into several regions, the various measures of length of these regions being multiplied by the sums of the various measurements of the width, and the figure thus obtained multiplied by the constant for the given region.. These constants have been worked out by the investigators and represent the reciprocal of the average factor for that particular combination of length and breadth measurements which showed the smallest variations.

In the formula proposed by Howland and Dana the data supplied, by Meeh and Lissauee were used. Meeh had included infants among his observations and Lissauer had measured the area of 11, making 14 in all. Howland and Dana first plotted on a chart the weight and surface area of these 14 cases and then drew a curve as nearly as possible to all these points so that the distance from any point would be as small as possible.

This curve (Fig. 12), by its distance from the axes ox and oy, represents an average of the observed data, so that when drawn to the proper scale, the point on the curve representing any known weight of the child may be marked on the chart and the surface area read off directly. Thus, if one has an infant weighing 7000 gm. and it is desired to know its surface area, one finds where the 7000 gm. line intersects the curve. Carrying this point horizontally to the left, it is seen to intersect the oy axis at a point corresponding to 4100 sq. cm.

This formula, u equals mx plus b, is the algebraic representation of this form of curve, and in it x and y represent the abscissas and ordinates of the curve, b represents the distance along the y axis, and m represents the tangent of the angle that the curve marked with the x axis.

In this formula:

y = surface area of child in square centimeters.

x = weight of child in grams.

m = 0.483

b = 750

The factor b was read directly from the chart and m was obtained by dividing 5560 minus 730 by 10,000. Having these last three quantities, it becomes possible to obtain the y or surface area by simple computation - the weight times 0.483 plus 730.

Pfaundler, in 1916, reviewed the previous methods of measuring body surface and elaborated a new method based on the principle that the body surfaces are usually in the form of a cylinder or obtuse cone. The body was divided into sixteen regions by use of an instrument- dermatograph, and the areas added to give the total surface. This instrument is illustrated in Fig. 13.

Respiratory Tract.-One of the most marked features of the premature and of the congenitally weak are the poor respiratory efforts, indeed, Billiard has defined congenital weakness as "the incomplete establishment of respiration." The premature in response to the need of air, inspires at birth, but its muscular power is weak and its efforts are insufficient to raise the thoracic wall and thus dilate the pulmonic cavity. As a result, though the large bronchi are filled with air, many of the small bronchioles are not dilated and a large portion of the lung continues to remain in a fetal stage, and may require several weeks for its complete expansion. The reason for this poor functioning of the organs of respiration lies in the lack of development of the respiratory centers in the medulla.

Most observers state that the chest wall of the premature infant is more or less immobile, moving but slightly with each respiration, but it has been our experience that quite constant evidence of prematurity is shown in the flexibility of the thorax and its tendency to retraction with each inspiration, the seeming immobility being the result of the poor effort on the part of the muscles of respiration, due to their weakness. The chest walls can expand but the muscular power is insufficient to make them do so. This muscular inertia, which is so well evidenced in these infants, is therefore partly the result of poorly developed muscles and partly the result of deficient innervation due to a similar lack of development of the cerebral centers.

Accompanying the deficient oxygenation of the blood are attacks of cyanosis, during which respiration ceases entirely. This apneic interval lasts for one or two minutes and then breathing is resumed. These attacks are not at all infrequent during the first fortnight and often appear without warning. In those cases in which recovery occurs the attacks become less frequent and less severe, but when unrelieved they are of grave significance and not uncommonly result fatally.

Clinically the weakened respirations_. are manifested by the monotonous, feeble, whining cry and grunting expirations with comparative immobility of the thorax, and the superficial and often irregular character of the respirations, which become abdominal in type. While a child born at the sixth month may breathe for hours or days, previous to that time respiration is not fully established. Even though respiratory exchange does not occur, the heart may be found beating several hours after birth.

The frequency of respiration in the sleeping premature immediately after birth is frequently as high as 40 to 50 per minute. When awake the rate is about 50 or more unless the infant is crying, when it is much less than in ordinary breathing. The type of respiration in the premature is essentially diaphragmatic, superficial and irregular, showing interruptions particularly during crying when these pauses may be quite long. The soft and yielding character of the thoracic wall in the premature permits of slight degrees of retraction of the lower intercostal spaces during the deeper inspirations.

The physical findings over the lungs of premature infants are uncertain. On inspection and palpation the thorax shows deficient mobility, on percussion the, sounds over the bases are lower than over the balance of the chest, and on auscultation the vesicular murmur is hardly perceptible. At autopsy these signs are confirmed and the lower parts of the lungs particularly are seen to be atelectatic, at times the major portion of the organ being involved, making gaseous interchange very difficult.

The complete establishment of respiration may be prevented not only by the weakness of the respiratory movements but by the aspiration of liquor amnii or mucus during the last moments of delivery, which mechanically prevents the entrance of air into the pulmonary alveoli. (See Atelectasis.)

Parrot, Billiard and others have noted a condition which is spoken of as life without respiration, of which the characteristic manifestations are the absence of thoracic movements, the presence of a pulse and of movements of the extremities, and the absence of asphyxia immediately after birth. The persistence of the ductus arteriosus renders this condition supportable, as it allows the blood to pass directly into the aortic current without passing through the lungs. Such infants remain in their intra-uterine state of apnea until the respiratory centers become sufficiently irritated by the increasing venous blood to evoke respiratory action. This life without respiration should not be confounded with the apparent death of children born at or before term. Apparent death has two forms: The syncopal form, which is characterized by pallor of the skin and absence of pulse, and the asphyxiated form, distinguished by cyanosis of the skin and the presence of a pulse beat. (See Apparent Death.)

The nasal passages of the new-born prematures are particularly narrow, favoring the easy occurrence of stenosis in inflammatory conditions involving the nasal mucosa.

Interference with respiration also results from the aspiration of food or vomited matter into the larynx or trachea, the lack of development of the pharyngeal and laryngeal reflexes being responsible for the not infrequent occurrence of this accident. Attempts at drinking sometimes result in mechanical hindrance of obstruction to inspiration during the act of swallowing. Aspiration of food is often followed by a pulmonary infection and thus atelactasis of the lung may be said to predispose to a pneumonia which not infrequently leads to death. (See Infections of the Lungs.)

Jaschke considers the deficient function of the respiratory apparatus as being due to the fact that the irritability of the respiratory center is so low that a large accumulation of carbonic acid in the blood is necessary to make it act. With the sinking of the carbonic-acid tension with stronger respirations, the depth of respiration decreases again, because of lowered stimulation of the respiratory center and finally a point is reached in which the blood is arterialized, when the respiratory center no longer responds. A pause in respiration sets in and lasts until excess of carbonic acid stimulates new respiratory movements.

A further point is brought out by Jaschke. There appears to be a disturbance of the gaseous interchange, which is probably explained by the peculiarity of the blood serum of debilitated premature infants. This was first noted by Pfaundler. The blood serum shows a diminution of the OH ions, and a correspondingly greater concentration of the H ions, which condition makes the draining of carbonic acid from the tissues more difficult. Jaschke believes that this agrees with Finkelstein's theory that the attacks of cyanosis are to be regarded as an expression of a chronic carbonic-acid intoxication.

The Digestive Tract.-1. Anatomy.-The muscles of the buccal region, of the tongue and of the soft palate are weak.

The stomach of the premature infant before its first feeding, as seen in autopsy, is in an almost vertical position and tubular in its form. In the premature infant which has been fed the fundus is fairly well developed and causes the stomach to assume a more oblique position. This is corroborated by a roentgen-ray examination (Figs. 14 and 15).

A. F. Hess was able to demonstrate that the gastric canal of the infant is more nearly vertical than horizontal, and that therefore from a functional standpoint the infant's food traverses the gastric canal in a vertical rather than a horizontal path, even though the stomach lies more or less horizontally. This fact is even more true of the physiological path of the food in the premature (Fig. 16).

The cardiac end of the stomach is found well to the left and usually about the level of the tenth dorsal vertebra. The cardiac sphincter is usually poorly developed (Fig. 17). This in part accounts for the ease with which the premature infant regurgitates its food. The pylorus lies somewhat higher than that of the full-term new-born, in whom it is found about midway between the ensiform cartilage and the umbilicus. Before feeding it is almost always found to the left of the median line. The pyloric musculature is usually quite well developed, even in the new-born premature (Figs. 18, 19 and 20).

The musculature of the stomach at autopsy in the new-born premature is in a state of contraction, giving the stomach a tubular appearance. In the living, however, this tubular appearance quickly disappears with the administration of food, the fundus enlarging much more rapidly than the balance of the stomach in order to meet the physiological demands.

Gastric Capacity.-Although many authors have measured the full-term infant's stomach as to its capacity, both at autopsy and in the living, their figures vary considerably.

Mosenthal, after a careful study of full-term infants measured during life and postmortem, states that the physiological capacity of the stomach exceeds the anatomical gastric capacity during life because of the rapid passage through the pylorus of the individual feedings during the act of nursing. This fact is corroborated by the roentgen ray (Fig. 16) in several of our cases. Therefore, the gastric capacity, as measured post mortem by filling the stomach with water under pressure of 15 cm. of water with the pyloric end of the stomach ligated, must also fall short of giving the exact functional capacity.

Pfaundler's figures for the stomach capacity during the first three months of life for the full-term infant are 90, 100 and 110 cc. Holt gives the following averages for stomach capacity in a series of studies made on infants dying during the first four weeks of life and examined postmortem.

Notwithstanding the fact that distention of the stomach according to the method of Pfaundler at autopsy is far from an ideal method of estimating the physiological capacity of the stomach, the author has undertaken to measure the stomach capacity for the various fetal ages after the sixth month by this method, and to illustrate the same graphically by photographs which represent the actual size of these stomachs at various fetal ages. This has been done more especially to illustrate the dangers of individual overfeedings which are so disastrous to the life of the premature.

Figs. 21 to 26 are photographs taken with specimens immersed in oil and represent the exact size of the stomach under 15 cm. of water pressure at different ages.

The stomach of the premature infant on a diet of breast milk is usually found empty at the end of one and one-half to two hours. That of the artificially fed requires a considerably longer period of time, depending upon the nature of the food administered, even in the case of feeding with predigested milk.

2. Physiology.-The digestive functions of the healthy premature infant are proportionate to the age at the time of birth. At the sixth or seventh month most of the functions and secretions are rudimentary and insufficient, while in the older infants the lessening of digestive ability is not so great.

The sucking ability in the prematures and weaklings is feeble as a result of the lack of muscular strength necessary to operate the suction, the muscles of the buccal region, of the tongue and of the soft palate being weak. Accompanying this muscular asthenia is an inactivity of the salivary glands, as a result of which the mouth is dry. The lack of sucking movements tends also to retard the development of these glands.

The strength to swallow is also diminished in the premature. In the weakest a few drops of milk placed in the mouth remain there; in the stronger, though at first they nurse, they soon tire and their efforts to swallow cease.

"Hunger contractions" were studied by Taylor in 5 premature and 40 full-term new-born infants. A comparison of the contractions in the new born with several older children showed that the hunger contractions in the former were greater than in the latter. Reflex inhibition from the presence of food in the stomach was present in infants of all ages. The time of appearance of hunger after feeding in healthy infants gaining in weight and receiving a sufficient amount of food was: For premature infants under one month, one hour and forty minutes; in full-term infants under two weeks, two hours and fifty minutes; in infants from two weeks to four months, three hours and forty minutes.

The ferments of the gastro-intestinal canal are most conveniently discussed from the standpoint of action. The first group are those that aid in the splitting up of protein substances.

Pepsin is present in the gastric mucosa as early as the fourth fetal month, though not in such quantities as in the older children. It increases in amounts up to about the third month of life and then remains at about that level. Hydrochloric acid and rennin are also present in fetal life. Hess was able to demonstrate free hydrochloric acid in 54 out of 55 cases immediately after birth.

Lipase was found to be present in small quantities by Ibrahim in a fetus of 800 gm. and plainly present in those from 1100 gm. upward Sedgwick had previously demonstrated it in 1906.

Trypsin is present in the pancreatic extract of the new born. Ibrahim found trypsinogen as early as the sixth fetal month and enterokinase was also found by him in an extract of intestinal mucosa from premature infants. The lower third of the small intestine is most active in the production of enterokinase.

Secretin, the ferment which activates the pancreas, was found in the small intestine of the full-term new born by Ibrahim and Gross, but its activity was slight. In the premature it is probably even more deficient.

Erepsin splits albumoses and peptones and originates from the mucosa of the small intestine. It has been demonstrated in the premature by Langstein, Jaeggis, Cohnheim and others.

The next group consists of the carbohydrate ferments, of which the milk-sugar ferment lactase is found in the intestinal contents, the stools and the intestinal mucosa. It is frequently absent from the intestinal tract of the premature, as it makes its appearance rather late in fetal life. Nothmann was able to demonstrate it in the stools of the mature new born in only a few cases. The presence of relatively large amounts of milk sugar in the infant's . food probably increases the amount and activity of the lactase. The deficiency of lactase at birth is indicated further by the finding of lactose in the urine of new-born infants (Nothmann). This would seem to point to a lack of milk-sugar fermentation (von Reuss).

The cane-sugar splitting ferments, invertin and saccharase, are present at an early date in embryonal life, although there is no use for them in those fed on human milk or where lactose is used artificially, for a long period of time. They are found in the intestinal walls and in the meconium.

Maltase is present, according to Ibrahim, in all parts of the small intestines and in the intestinal contents of prematures. Diastase, the amylolytic ferment, is present in the salivary glands and in the pancreas of the new born. Ptyalin is found in the parotid and in the submaxillary secretions, although it is not required until the beginning of the starch feeding. Ibrahim believes that the pancreatic function of the new born and especially of the premature new born is somewhat below that of the older infant, and, therefore, the instructions of the older clinicians not to feed these infants mixtures containing much starch were correct from a physiological point of view (von Reuss).

The third and last group of. ferments are those which act upon the fats. Steapsin was found in the pancreatic secretion by Zweifel, and Ibrahim showed that it was also present in the premature. The meconium contains this ferment. Lipase is very active in the gastric mucosa of prematures.

In general the premature may be said to possess nearly all the ferments necessary for the breaking-down of its food. Some of them, such as diastase and ptyalin, which are not. present during fetal life or only in the most insignificant quantities, are called forth even in the premature, by the administration of food, and though they may be deficient both in amount and in activity at this time, the continued stimulation offered by food soon results in a material increase in both qualities, at least in the case of prematures who possess a sufficient degree of vitality. All necessary ferments being present, it is of little advantage to feed the premature infant predigested human milk.

Ferment therapy also is of little value in premature infants as is also true in older children. If the required ferments are present they will increase with the giving -of food. It is not the absence of ferments that is responsible for the peculiarities of action of the digestion of the prematures, but rather the way the food is broken down and absorbed; and a clear realization of these differences is necessary to an understanding of the peculiarities of the digestion of the new born, both premature and at term.

The normal gastric mucosa provides only for the absorption of salts and carbohydrates.

Ganghofer and Langer' found that up to the fourth day of life the intestinal tract is permeable to foreign proteins and the importance of this is great. The permeation of. these through the intestinal wall results in the formation of antibodies in the tissues, and the danger of sensitization of the organism to that particular protein. Herein lies one of our most important indications for feeding with human milk.

The intestinal canal is more frail than in the full-term infants and the intestinal musculature is weak and easily distended and often times unable to expel the contained meconium.

The meconium begins to be formed at the fourth fetal month. It is made up of the secretions of the gastro-intestinal tract, vernix caseosa, threads of mucus, desquamated epithelium, biliary acids and salts, cholesterol, fat droplets, fatty-acid crystals and liquor amnii which has been swallowed. That which is passed on the first day is dark green; thick, sticky, homogeneous and odorless. Its excretion lasts from twenty-four to ninety-six hours. During the first few hours it is free from bacteria and even later the number of organisms present is small. The characteristic yellow color of the breast milk stool is scarcely established before the fifth and sixth day and then only when the milk taken is rich. The sour odor of the breast-milk stool may also be recognized at this time.

Hymanson and Kahn, investigating the properties of meconium found that there were traces of ammonia and amylase, but no uric acid, trypsin, erepsin, lactase or lipase. Their analysis of the inorganic constituents is given in the table which follows: