OF LACTATION. 1023 



that entered into the original composition of the milk ; this may be readily 

 separated by evaporation. When Milk is examined with the Microscope, it is 

 seen to contain a large number of particles of irregular size and form, suspended 

 in a somewhat turbid fluid ; these particles vary in size from about the 1-12, 700th 

 to the 1 -3040th of an inch ; and they are termed " milk-globules." They are 

 not affected by the mere contact of ether or alkalies ; but if these reagents are 

 shaken with them, an immediate solution is the result. The same effect happens 

 if they are first treated with acetic acid. Hence it is evident that the globules 

 consist of oily matter, inclosed in an envelop of some kind : and an extremely 

 delicate pellicle may in fact be distinguished, after the removal of the oily 

 matter by ether, or after the globules have been ruptured and their contents 

 pressed out by rubbing a drop of milk between two plates of glass. No proof 

 of the organization of this pellicle has, however, been detected ; and it is probably 

 to be regarded as the simple result of the contact of oil with albuminous matter 

 ( 42). Besides these milk-globules, other globules of much smaller size are seen 

 in milk ; and these present the peculiar movement which is exhibited by mole- 

 cules in general. Most of them seem to consist of oily matter not inclosed in an 

 envelop, as they are at once dissolved when the fluid is treated with ether ; 

 but, according to the statements of Donne, it would seem that a portion of them 

 are composed of casein, suspended, not dissolved, in the fluid. In addition to 

 the foregoing particles, there are found in the Colostrum, or milk first secreted 

 after delivery, large yellow granulated corpuscles, which seem to be composed 

 of a multitude of small grains aggregated together ; these appear to be chiefly 

 of a fatty nature, being for the most part soluble in ether ; but traces of some 

 adhesive matter, probably mucus, holding together the particles, are then seen. 

 They are considered by some as " exudation-corpuscles," to which they certainly 

 bear a close resemblance ; according to Reinhardt, they are transformations of 

 the epithelial cells of the mammary ducts, the result of a sort of fatty degene- 

 ration or regressive metamorphosis consequent upon the peculiar activity of the 

 mammary gland during pregnancy. 1 Lamellae of epithelium are also found in 

 the milk. All the larger globules may be removed by repeated filtration ; and 

 the fluid is then nearly transparent. This, in fact, is the simplest way of sepa- 

 rating the oleaginous from the other constituents of the milk; as but little 

 casein then adheres to the former. That the transparent fluid which has passed 

 through the filter contains nearly the whole amount of the casein of the milk, 

 appears a sufficient proof that this is, for the most part, truly dissolved in the 

 fluid. 



1024. "We shall now consider the chemical characters of each of the fore- 

 going ingredients. The Oleaginous matter of milk principally consists of the 

 ordinary components of fat ( 37) ; but it also contains another substance pecu- 

 liar to it, designated as butyrin, to which the peculiar smell and taste of butter 

 are due; this yields in saponification three volatile acids, of strong animal odor, 

 to which Chevreul has given the names of butyric, caproic, and capric acids. 

 These peculiar acids are not only formed when the butyrin is treated with alka- 

 lies, but are produced by the ordinary decomposition of this principle, which is 

 favored by time and moderate warmth. The Casein of Human milk, however, 

 is usually said to be much less precipitable by acids than is that of the Cow ; 

 very commonly resisting the action of the mineral acids, and even that of the 

 acetic, but being always coagulated by rennet, though the curd is long in col- 

 lecting. On this point, however, there has been much discrepancy of statement, 

 on which the recent experiments of Mr. Moore 2 throw some light. It appears, 

 from the results obtained by him, that Human Milk forms with most acids two 



1 See an abstract of his views in the "Edinb. Monthly Journal" for Feb. 1848. 



2 "Dublin Quarterly Journal of Medical Science," vol. vii. p. 280. 



