MAMMARY GLANDS SECRETION OF MILK. 653 



857. It is very interesting to observe that Milk contains the three classes 

 of principles which are required for human food, the Albuminous, Oleagi- 

 nous, and Saccharine ; and it is the only secreted fluid, in which these all 

 exist in any considerable amount. It is, therefore, the food most perfectly 

 adapted for the young animal; and is the only single article supplied by na- 

 ture, in which such a combination exists. Our artificial combinations will be 

 suitable to replace it, just in proportion as they imitate its character; but in 

 none of them can we advantageously dispense with milk, under some form 

 or other. It should be remembered that the saline ingredients of Milk, espe- 

 cially the phosphates of lime, magnesia, and iron, have a very important 

 function in the nutrition of the infant, affording the material for the consoli- 

 dation of its bones, and for the production of its red blood-corpuscles; and 

 any fluid substituted for milk, which does not contain these, is deficient in 

 essential constituents. It is very justly remarked by Dr. Rees, that of all 

 the secreted fluids, Milk is most nearly allied in its composition to blood. 



858. The proportion of the different ingredients in the Milk of different 

 animals, is subject to considerable variation : and this fact is of much practi- 

 cal importance in guiding our selection, when good Human milk cannot be 

 conveniently obtained for the nourishment of an infant. The first point to 

 be inquired into, is the quantity of solid matter contained in each kind ; this 

 may be determined either by evaporation, or by the specific gravity of the 

 fluid. The Specific Gravity of Human milk is stated by Dr. Rees to vary 

 between 1030 and 1035; others, however, have estimated it much lower. 

 That of the Cow appears to be usually about the same ; that of the cream, 

 however, being 1024, and that of the skimmed milk about 1035. The varia- 

 tion will in part depend (as in the case of the urine) upon the quantity of fluid 

 ingested, and in part, it is probable, upon the manner in which the milk is 

 drawn ; for it is well known to milkers, that the last milk they obtain is much 

 richer than that with which the udder is distended at the commencement. 

 The quantity of solid matter, obtainable from Human and from Cow's Milk 

 by evaporation, seems, like the specific gravities of the fluids, to be nearly the 

 same. In the relative proportion of the ingredients, however, there is a con- 

 siderable difference ; there being much more sugar, and less caseine in Human 

 Milk than in that of the Cow. The following table exhibits the relative pro- 

 portion of the different ingredients, in the Milk of various animals, from which 

 it is commonly obtained: 



Cow. Goat. Sheep. Ass. Mare. 



Water ..... 861-0 868-0 856-2 907-0 S96-3 



Butter . ... 38-0 33-2 42-0 12-10 traces 



Caseine . . 68'0 40'2 45-0 16-74 162 



Sugar of Milk and Extractive Matters . 29-0 52-8 .00-0 ) 



Fixed Salts . . . .6-1 5-8 6-85 



It appears from this, that, whilst the milk of the Cow, Goat, and Sheep do 

 not differ from each other in any very prominent degree, that of the Ass and 

 Mare is a fluid of very dissimilar character, containing a comparatively small 

 proportion of caseine and butter, and abounding in sugar. Hence it is, that 

 it is much more disposed to ferment than other milk ; indeed the sugar of 

 Mare's milk is so abundant, that the Tartars prepare from it a spirituous 

 liquor, to which they give the name of koumiss. It appears from these de- 

 tails that no milk more nearly approaches that of the Human female, than 

 that of the Sheep and Goat ; these both possess, however, a larger proportion 

 of caseine, which forms a peculiarly dense curd ; and the milk of the Goat 



retina, sometimes proceeding to complete amaurosis ; this, if treated in time, is most commonly 

 relieved by discontinuance of lactation, generous diet, and quinine. 



55* 



