MAMMARY GLANDS SECRETION OF MILK. 651 



a state of change ; whether from their own decomposition, or from incipient coagulation; 

 either of which might have taken place during the processes of filtration, &c., that were 

 required to determine their nature. In addition to the foregoing particles, there are found in 

 the Colostrum, or milk first secreted after delivery, large yellow granulated corpuscles, which 

 are described by Donne as composed of a multitude of small grains aggregated together, and 

 frequently including a true globule of milk in their centre: these are for the most part solu- 

 ble in ether; but traces of some adhesive matter, probably mucus, holding together the par- 

 ticles, are then seen. They are considered by some as exudation-corpuscles; to which they 

 certainly bear a close resemblance. Lamella? 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 separating the oleaginous from the other 

 constituents of the milk; as little caseine then adheres to the former. That the transparent 

 fluid which has passed through the filter contains nearly the whole amount of the caseine 

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

 fluid. 



b. We shall now consider the chemical characters of each of the foregoing ingredients. 

 The Oleaginous matter of milk principally consists, like fatty matter in general, of the two 

 substances, elaine and stearine; which are converted in the process of saponification into 

 the elaic, stearic, and margaric acids: but it also contains another substance peculiar to it, 

 which yields in saponification three volatile acids, of strong animal odour, to which Chev- 

 reul has given the names of butyric, caproic, and capric acids ; whilst the fatty substance 

 itself, to which the peculiar smell and taste of butter are due, is designated as butyrine. The 

 peculiar acids are not only formed when the butyrine is treated with alkalies; but are pro- 

 duced by the ordinary decomposition of this principle, which is favoured by time and mode- 

 rate warmth. The Caseine or cheesy matter of milk, which is obtained with some slight 

 admixture of fatty matter in the production of cheese from skimmed milk, is chiefly distin- 

 guished from Albumen, by the peculiar readiness with which it is precipitated by feeble 

 organic acids, such as the lactic and acetic ; and by its non-coagulability by heat alone. The 

 Caseine of Human milk, however, is 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 collecting. It is remarked 

 by Dr. G. 0. Rees,* that the caseine of human milk thus bears somewhat the same relation 

 to that of the cow, that the albumen of chyle bears to that of the blood. The Sugar of milk, 

 which may be obtained by evaporating whey to the consistence of a syrup and then setting 

 it aside to crystallize, contains a large proportion (12 per cent.) of water, so that it may be 

 considered as really a hydrate of sugar; it is nearly identical in its composition with starch, 

 and may, like it, be converted into true sugar by the action of sulphuric acid ; and when in 

 contact with a ferment, or decomposing azotized compound, it is extremely prone to be con- 

 verted into lactic acid, by appropriating to itself the elements of water. It is, in fact, through 

 this process, that the coagulation of the caseine is effected, by means of rennet ; for as soon 

 as a very minute quantity of lactic acid is generated, it withdraws from the caseine the free 

 alkali which kept it in solution, and the caseine is consequently precipitated. The same 

 effect will be produced by incipient decomposition of the caseine itself; which will soon 

 occasion lactic acid to be generated from the sugar, in sufficient quantity to give to the rnilk 

 a distinctly acid reaction. The Saline matter contained in milk, appears to be nearly iden- 

 tical with that of the blood; with a larger proportion of the phosphates of lime and mag- 

 nesia, which amount to 2 or 2j parts in 1000. These phosphates are held in solution chiefly 

 by the Caseine; which seems to have a power of combining with them, even greater than 

 that of Albumen: the presence of a minute proportion of free alkali, also, assists their solu- 

 tion. A small portion of iron in the state of phosphate, together with the chlorides of 

 potassium and sodium, may also be detected in milk.f 



855. The proportion of these different constituents is liable to great varia- 

 tion, from several causes. Thus, the whole amount of the solid constituents 

 may vary from 86 to 138'6 parts in 1000; the difference being partly due to 

 individual constitution, but in great part, also, to the amount and character 

 of the ingesta. The average seems to be between 100 and 120 parts. The 

 following are the results of the analyses of Simon; the first column being 

 the average of fourteen observations upon the same woman ; the second giv- 

 ing the maximum of each ingredient; and the third the minimum: 



Art. MILK, in the Cyclopaedia of Anatomy and Physiology, 

 t Haidlen, in Annalen der Chemie und Pharmacie, xlv. p. 263. 



