MAMMARY SECRETION ITS COMPOSITION. 975 



being 42.4 of casein and 30.6 of albumen. 1 If it be kept long enough, a 

 spontaneous change takes place in its composition ; the sugar is converted 

 into lactic acid, and this coagulates the casein, precipitating it in small 

 flakes. The same precipitation may be accomplished at any time by the 

 addition of an acid ; all the acids, however, which act upon albumen, do 

 not precipitate casein, as will presently be pointed out in detail ; the most 

 effectual is that contained in the dried stomach of a calf, known as rennet. 

 The whey left after the curd has been separated contains a large proportion 

 of the saccharine and saline matter that entered into the original composi- 

 tion of the milk ; this may be readily separated by evaporation. 



812. 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 some- 

 what turbid fluid (Fig. 370); these particles vary in size from about the 

 TV: toftth to tne 3oV? tu f an i ncn ! ail d 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 immedjate 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 envelope 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 rup- 

 tured 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. 2 Besides these milk-globules, other 

 globules of much smaller size are seen in milk; and these present the pecu- 

 liar movement which is exhibited by molecules in general. Most of them 

 seem to consist of oily matter not inclosed in an envelope, 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. The colostrum, or milk secreted 

 during the first week after delivery, is described by Dr. Davy, in the case of 

 the cow, as being of a rich yellow color, less fluid than the milk of a later 

 period, of a higher specific gravity (1075), slightly acid, and containing 

 large oil-globules, a few irregular flakes, probably epithelium scales, a little 

 granular matter like curd, and a small number of granular corpuscles, the 

 largest of which are about the -^Jo^ f an ^ uc ^ ' u diameter (Fig. 370, a a). 

 It coagulates on being heated to about 163 F. 3 The granular corpuscles, 

 when maintained at a temperature of J00 F., exhibit feeble amoeboid 

 movements (Strieker and Schwarz). They are probably epithelial cells of 

 the mammary ducts which have undergone fatty degeneration.* The chemi- 

 cal composition of the solids of the colostrum, as compared with the milk of 

 a subsequent period, is well given in the following percentage table by Dr. 

 Tolmatscheff: 5 



Age. Temperament. Albumen Fat " Sll g ar - 



1 For a discussion on the resemblances and differences between Casein and Alkali- 

 albuminate, see Soxlet, Journ. f. Pract. Chemie, 1872, Bd. vi, p. 1. 



2 The presence of an albuminous envelope to the oil-globules floating in milk hag 

 been called in question by Kehrer, Archiv f. Gynaecol., Bd. ii, 1871, p. 1 (see also 

 Zuhn, Pfliiger's Archiv, 18G9, p. 598), but is maintained by Schwalbe, Max Schultze's 

 Archiv, Bd. viii, p. 269. 



3 See also Bernard, Le?ons, vol. ii, 1859, p. 224. 



4 See Reinhardt, Abstract in Edin. Journ., Feb. 1848. 



5 Hoppe-Seyler, Med. Chem. Unters., 1867, p. 272. 



