THE MILK. 435 



From the fact that the coagulum which results in cows' milk 

 upon the addition of chymosin is much tougher and denser than 

 that which is obtained with human milk, it has been concluded that 

 the caseinogen of the two is not identical. Soxhlet, however, has 

 shown that the density of the coagulum is primarily dependent upon 

 the concentration of the caseinogen solution and the amount of 

 soluble calcium salts and acid phosphates present. As this is much 

 greater in cows' milk than in human milk, it follows that marked 

 differences must thus exist. There is evidence to show, neverthe- 

 less, that different forms of caseinogen occur. Elementary analysis 

 of human caseinogen (Hammarsten) and cows' caseinogen (Wro- 

 blewski) has given the following results : 



Human, C, 52.96 ; H, 7.05 ; N, 15.65 ; S, 0.75 ; P, 0.84 ; O, 22.78 per cent. 

 Cows', C, 52.24; H, 7.32; N, 14.97; S, 1.11; P, 0.68; O, 23.66 " " 



The difference is here especially noticeable in the amount of sul- 

 phur. Human caseinogen, moreover, is not so readily precipitated 

 by salting or by the addition of acids, and does not always coagulate 

 with chymosin. The gastric juice, it is true, can precipitate the 

 substance, but it readily dissolves in an excess without leaving any 

 residue of nuclein. From this observation Szontagh has concluded 

 that human caseinogen is in reality no nucleo-albumin. But aside 

 from these data we have abundant evidence that human caseinogen 

 and cows' caseinogen are not identical, in the fact that no modifica- 

 tion of cows' milk, however produced, is so readily digested by the 

 infant as is human milk. 



Like all albumins, caseinogen is optically active ; its specific rota- 

 tion in neutral solution is 80 degrees. 



The isolation of the caseinogen from milk will be described below, 

 in association with the isolation of the soluble albumins. These, as 

 I have already said, are lactalbumin and lactoglobulin. 



LACTALBUMIN. Lactalbumin is found both in human milk and 

 cows' milk, and is manifestly closely related to the common serum- 

 albumin of the blood-plasma. Its specific rotation, however, is 

 markedly less, viz., 37 degrees, as compared with 62.6 to 64.6 

 degrees. Its composition according to Sebelien is C, 52.19 per cent. ; 

 H, 7.18 ; N. 15.77 ; S, 1.73 ; and O, 23.13 ; while that of serum- 

 albumin is given as C, 52.25-53.06 per cent. ; H, 6.65-6.85 ; N, 

 15.88-16.04; S, 1.8-2.25; and O, 22.25-22.97 (Hammarsten). 



LACTOGLOBULIN. The lactoglobulin which has been isolated 

 from cows' milk seems to be identical with the serum-globulin 

 of the blood. It requires no further description. 



That still other albuminous substances may occur in the milk is 

 possible ; but if so, they are present only in traces and have not as 

 yet been identified. Albumoses and peptones are not found in 

 fresh milk. According to Siegfried, a phosphor-earn ic acid can be 

 isolated from milk after removal of the casein and the coagulable 

 albumins ; this, however, is supposedly not identical with that found 

 in muscle-plasma. 



