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On Human Milk

By C. Meymott Tidy, M.B.

London Hospital, Whitechapel, London, England.

Published in
Clinical Lectures and Reports by the Medical and
Surgical Staff of the London Hospital
, 4:77-84, 1868.

 

Milk has always been regarded as a model food. For upon this diet, prepared by nature without the hand of the adulterator, elaborated expressly for one object, the child, and, in short, all the young of the mammalia, live, grow, and thrive. Regarding milk in this light (and we are correct in doing so) as a model food, and the only model food, its analysis becomes a matter of no little practical and physiological interest, inasmuch as upon it we are enabled to lay the foundation of all systems of diet. Here we find casein as the representative of the azotised or albuminous group; the butter of the oleaginous; the sugar of the saccharine; the acqueous; and the various salts of the earths and alkaline earths are representatives of the saline variety of alimentary substances. And these principles, and in their due proportion, must constitute not merely the food of the young child, but the food of the full-grown man too, when he has long ceased to be

The infant,
Muling and puking in the nurse's arms.

Human milk is described as a white, fatty, and rather thick fluid. But with respect to its colour, I have noticed it of a deep yellow, and occasionally, though much less frequently, of a decided blue tinge. And these varieties of colour are not so much dependent as some seem to have imagined upon peculiarities of diet as upon disordered states of the system. After being allowed to stand for some time woman's milk, like that of the cow, separates into two layers. The greater part of the fatty matter rises to the surface and constitutes the cream; the remainder forming the skim-milk, which is not white and opaque like that of the cow, but nearly translucent. Upon examining human milk under the microscope, we see that it consists of numerous, highly refracting, transparent oil and fat globules floating in a clear liquid. On the addition of a little dilute acetic acid, we shall discover a thin membrane investing these globules. We find a considerable variety in the size of these fat vesicles, even in the same milk, and it is curious to note how their size is modified by disease. Those of human milk are rather larger than those of the milk of animals, and those in asses' milk decidedly smaller than any seen in that of other animals.

Human milk has a specific gravity varying from 1.027 to 1.034. Some have stated it as high as 1.042. I regret I have not taken the specific gravity of every specimen I have analysed; but the following table represents the results of twenty analyses, giving 1.030 as the average of the whole.

Table of Specific Gravities of Human Milk.

1.032

1.034

1.028

1.032

1.028

1.028

1.034

1.033

1.029

1.032

1.029

1.027

1.031

1.028

1.034

1.031

1.029

1.034

1.034

1.031

Healthy milk has generally a distinct alkaline reaction, but human milk is peculiar in retaining this alkalinity for a much longer period than the milk of other animals. Sometimes I have found it alkaline after standing for four days, but as a rule it shows an acid reaction in about forty hours, the milk of a cow rarely retaining its normal alkaline state over ten hours, and as far as I have been able to judge, goat's and ewe's milk a still shorter period. I have upon two occasions noticed asses' milk to be slightly acid even when fresh drawn. Although it is not the immediate subject of the present paper, I may remark in passing, that the degree of alkalinity and the time it remains alkaline are curiously modified by disease. Indeed, in some morbid states of the system, I have been doubtful whether there was at the first any alkaline reaction whatever, and in one case it was certainly slightly acid.

The composition of milk has been very differently stated by various chemists; and this no doubt arises, at any rate primarily, from the difficulties that present themselves in making a successful analysis. The first process of producing complete desiccation is no easy matter, as the temperature must be sufficient to drive off the water, but not so great as to decompose the butter. Numerous modes have been proposed for the analysis of milk. I have adopted as a rule the method originally planned by Dr. Simon, with one or two slight modifications, viz., evaporating to dryness with great care a known weight of the milk, removing the fat by treating the residue with twelve or fourteen times its bulk of boiling sulphuric ether, digesting the residue with boiling water and precipitating the casein by rennet; finally, estimating the fixed salts by incinerating a weighed quantity of the dried residue. I am aware that objections may be urged to this method of procedure, still on the whole I am inclined to think it yields better results than any other course that has been proposed.

I will now give a table of thirteen analyses, representing the composition of 1,000 parts of healthy human milk that I have lately made, and also I shall add the average of the thirteen experiments.

Table of Results of Thirteen Analyses of Healthy Human Milk.

Average

Water

889.26

876.76

870.88

868.52

886.06

881.36

888.02

877.19

885.04

869.09

884.20

849.59

888.86

878.06

Solid Constituents

110.74

123.24

129.12

131.48

113.94

118.64

111.98

122.81

114.96

130.91

115.80

150.41

111.14

121.93

Fat

44.48

38.86

40.42

40.73

41.63

35.71

26.42

42.63

33.81

43.16

37.47

51.84

45.63

40.21

Casein

29.68

35.33

29.21

39.48

29.98

38.42

34.61

32.82

35.20

31.61

32.68

43.61

35.42

35.23

Sugar, &c.

32.90

46.24

55.60

48.31

39.24

41.23

48.23

43.04

42.79

52.48

42.97

34.28

27.18

42.65

Salts

3.80

2.96

3.10

2.51

3.00

2.83

2.36

3.26

2.34

3.60

2.50

2.30

2.48

2.85

With respect to the salts in human milk, they consist chiefly of phophates of lime, soda, magnesia, and iron, carbonate of lime, chlorides of potassium and sodium. Some have mentioned sulphate of potash, but I have never succeeded in detecting it.

We frequently hear milk defined as "a secretion produced by the mammary gland of the female animal after giving birth to its young," or words at any rate equivalent to asserting that the formation of milk is the result of pregnancy. But it is an interesting question whether the secretion of this fluid is after all dependent upon any blood condition peculiar to the pregnant state. I am inclined to think the existence of milk in the mammae of males somewhat commoner than is generally believed. It is very frequent to see infants with their breasts freely distended with fluid of a milky nature, and some practitioners of experience have informed me that they have noticed this state of the mammae of new-born infants to be as common in males as in females. I have read somewhere, I think in Humboldt's works, of an Indian who suckled his infant child for five months after the death of his wife, the milk increasing in quantity as the child grew older. Such stories are not uncommon. It is an undoubted fact, however, that the secretion of milk in males is a more frequent occurrence amongst the blacks, and the inhabitants of tropical parts, than in our own country, and I have noticed moreover that as a rule the mammae of blacks are somewhat more developed than those of Europeans. But further, women who have never had children sometimes have milk freely secreted. I have been told that the white people in Jamaica frequently seek for black single women who have milk in their breasts to nurse their infants, and it is by no means difficult to find such. I may here mention the particulars of a curious case that occurred in my father's practice. A lady a short time back consulted him respecting her daughter whom she suspected of being in the family-way. The suspicion was founded in the circumstance that there was a large quantity of milk in the breasts. The young lady, of course, indignantly denied these imputations on her character, and time proved that the suspicions were unfounded. The existence, however, of such a copious supply of milk was explained in the following way:-- Her sister had died a few days after her confinement, and she had very properly undertaken to take charge of her infant niece, the child slept with her, and by that peculiar "instinct," as Cuvier termed it, the infant at night-time, prompted by hunger, found its way to its aunt's nipple, which desire she very foolishly gratified. This occurred for two or three nights running, the result being as I have stated, the milk being so freely secreted, that she was able afterwards to suckle the child, a somewhat awkward duty it must be admitted for a young single lady to undertake. Such cases seem to favour the notion that whilst the supply of milk is generally the result of pregnancy, it is not necessarily so, external irritation being of itself sufficient to develope milk in the breasts. The facts then seem to me to be these, that both in male and female, the elements of milk and the means for the transformation of these elements are present, but whether they are to be so transformed will depend not altogether upon the existence of pregnancy, but upon other and various exciting causes, producing a general development of the mammary glands.

I have for some time past been endeavouring to collect sufficient milk from a male animal, for analysis, but I have not at present been successful. I have frequently, however, found milk, or at any rate a fluid having the colour, taste, and general appearance of milk, as also the same microscopic appearance, only that I have noticed the fat vesicles were smaller and less in quantity than ordinarily; but there has never been enough of it for analysis. Liebig has given an account of a he-goat that had a copious secretion of milk, in this case, however, it was accustomed to suckle itself, and not its kids. The animal was four years old (scarcely, one would think, requiring a milk diet), the genitals were well developed, and many females had been impregnated by it during the previous autumn. In 1,000 pints of milk he found

Water

850.9

Casein

96.6

Sugar

26.0

Butter

26.5

It gave, on incineration, 7.82 ashes in 1000 grs. of 100 pints, of which 41.6 were insoluble, and 58.4 soluble in water.

I have several times analysed goat's milk, and give below the average of my experiments, which differed so very slightly, that it is scarcely necessary to state the separate analysis of each.

Water

845.81

Solid Constituents

154.19

Butter

33.94

Casein

65.87

Sugar

49.96

Salts

5.60

We may note, therefore, that the milk of the he-goat yielded a far larger amount of casein, but less butter and sugar than is found in the milk of the female goat.

The first milk formed after delivery, termed the colostrum, is considerably thicker, sweeter, and of a deeper colour than that afterwards secreted. There is not a doubt that it has a peculiar purgative action upon the infant, supposed by some to be due to the increased quantity of the salts, though, according to my analysis, this increase is very trifling. Nature has designed this laxative action of the colostrum, to rid the infant of the meconium. And yet, some nurses will persist in drawing it off, to substitute in its place a teaspoonful of castor-oil.

Nature, we may depend upon it, is the best judge after all. We find also, some differences in the microscopic appearance of the colostrum. In addition to the oil-globules, which are far more numerous and larger than usual, some granulated corpuscles are to be seen (first pointed out and described by M. Donné), and which vary much in size and shape, and are generally of a yellow colour. M. Donné states he has found these granular bodies as late as the 28th day after delivery. I have seen them three times on the 7th day, and once on the 9th, but never later, though I have over and over again looked for them. The analysis of the colostrum presents marked differences from that of ordinary milk. There is a very much larger amount of solid constituents, and albumen is also present in human colostrum, but nothing like the quantity that is to be found in that of the cow. I may here mention, that I see from my note-book that each specimen of the colostrum I examined was after a first confinement; I have placed the ages of the women at the top of each analysis. They are as usual, reckoned in 1,000 parts.

Age 29.

Age 17.

Age 21.

Average of
Three
Experiments.

Water

842.07

857.87

822.38

840.77

Solid Constituents

157.93

142.13

177.62

159.22

Fat

53.70

55.85

63.90

57.81

Casein

33.60

32.15

31.11

32.28

Sugar

66.03

50.72

78.65

65.13

Salts

Soluble

Insoluble

3.32

3.92

.60

2.20

2.88

.68

2.96

3.81

.85

2.82

3.53

.71

I will now give the result of four experiments made within the seventh and twelfth days after delivery, when the milk is beginning to assume its normal state. The sugar and fat still remain in somewhat larger quantity than is usual. The casein seem to decrease in quantity during the first wee, after which it gradually increases, whilst the amount of the sugar and fat diminishes in quantity.

Analysis of Four Samples of Human Milk from the
Seventh to the Twelfth Day After Delivery

Average
of Four
Analyses.

Water

850.40

877.66

862.58

860.22

862.71

Solid Constituents

149.60

122.34

137.42

139.78

137.28

Fat

69.15

42.41

51.85

51.40

53.70

Casein

29.60

25.35

32.15

30.91

29.50

Sugar

48.36

51.83

50.72

54.54

51.36

Salts

2.01

2.60

2.10

2.18

2.23

I have endeavoured to draw out a table to shew the difference in composition between human milk and that of some animals.

Human.

Cows'.

Goats'.

Ewes'.*

Asses'.*

Water

878.06

851.76

845.81

856.2

916.3

Solid Constituents

121.93

148.24

154.19

83.5

Fat

40.21

35.67

33.94

42.0

1.1

Casein

35.23

58.43

65.87

45.0

8.2

Sugar

42.65

47.64

49.96

50.0

60.8

Salts

2.85

6.40

5.60

6.8

3.4

* Chevalier and Henri.

I have never made a chemical analysis of either asses' or ewe's milk, but have given those of Chevalier and Henri. Cows' milk contains a larger amount of solid constituents than human milk; goats' milk contains a larger amount of casein than any other milk, and a larger quantity of sugar than either human or cows' milk. According to Chevalier asses' milk only contains 1.1 part of fat in 1,000.0 and a very large quantity of sugar. I had hoped before finishing this paper to have made an analysis of asses' milk, but regret my time has not allowed me to do so.

After a woman has taken a full dose of any medicinal reagent, I have never succeeded in detecting the least trace of it in the milk, and yet we know that, by administering mercury to the mother, syphilis is cured in the suckling, and that purgatives given in this way will affect the child. Four substances (all easily detected) were tried; viz., iodide of potassium, ferrocyanide of potassium, sulphate of magnesia, and chloride of mercury (corrosive sublimate), which a patient had been taking for upwards of a week. And in neither case could I detect the slightest trace of these salts in the milk, and yet practically we know they have an effect on the infant. They are, therefore, probably present in some new guise. I am at the present time occupied in attempting to discover in what form they are present. Whatever is given, certainly undergoes remarkable changes, a gracious act of nature doubtless, that the tender frame of the infant should not be dependent upon everything the mother may take, and which might prove injurious if not poisonous to her offspring. These experiments, and the modifications of milk, induced by certain diseased states of the system, I hope to deal with on some future occasion.

I should here express my best thanks to many friends who have assisted me to obtain specimens of milk for analysis. Amongst others, I must mention Mr. Smart and Dr. E. H. Moore, who have allowed me every facility of obtaining specimens from the maternity department of the Bethnal Green Workhouse.


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