THE PROTEIDS OF MILK. 139 



clot with rennet at all ; when it does so, the clot is a fiocculent 

 precipitate, which frequently redissolves rapidly in excess of gastric 

 juice. According to Szontagh, 1 human caseinogen yields no pseudo-nuclein 

 on gastric digestion; this was confirmed by Wroblewski, 2 who found 

 also that human caseinogen has the following percentage composition 

 C, 52-24; H, 7'31 ; N, 14-9; P, 0-68; S, 1117; 0, 23'66. This, it will 

 be seen, is different from the composition of the caseinogen of cows' milk. 

 Human caseinogen contains phosphorus, but not in the form of pseudo- 

 nuclein, as in cows' milk. 



Wroblewski finds that human milk contains small quantities of lact-albnmin, 

 and of another proteid very rich in sulphur (4*7 per cent.) and poor in carbon 

 (45 '01 per cent.). Lehmann and Hempel 3 find that the caseinogen of cows' 

 milk contains 7 '2 per cent, of ash; this consists of CaO, 49*5; MgO, 2'4; 

 Po0 5 , 47 '0 ; and S0 3 1 '06 per cent. The elementary composition of the 

 proteid is given as C, 50'86 ; H, 672 ; N, 14'63 ; P, 0-81 ; S, 0'72 ; ash, 6-47 

 per cent. The caseinogen of woman's milk contains more sulphur, 1*09, and 

 less ash, 3*2 per cent. Some of the differences between the two caseinogens 

 are doubtless dependent on the amount and nature of the ash with which they 

 are associated. 



The occurrence of nucleon (phospho-carmc acid) in milk has already been 

 mentioned on p. 104. Siegfried 4 states that the nucleon accounts for 41 -5 per 

 cent, of the phosphorus in human milk, but for only 6 per cent, of that in 

 cows' milk. Practically all the phosphorus in human milk is in organic com- 

 bination (nucleon and caseinogen). 



Lad-albumin. After the precipitation of caseinogen and lacto- 

 globulin by half-saturation with ammonium sulphate, lact-albumium re- 

 mains in solution. It can be incompletely precipitated from this solution 

 by saturation with sodium sulphate. It is completely precipitated with 

 the other proteids when milk is saturated with ammonium sulphate. It 

 coagulates between 70 and 80 C. ; in cows' milk at 77 C. It is not 

 separable, like serum albumin and egg albumin, into several proteids by 

 fractional heat coagulation. It, moreover, is coagulated by heat very 

 slowly; the solution must be kept some hours at 77 C., before it is 

 completely precipitated. Its specific rotatory power 5 D = -36, i.e. less 

 than that of serum albumin ; it has the following percentage composi- 

 tion : C, 5219; H, 718; N, 15-77; S, 1-73; 0, 23-13. The high 

 percentage of sulphur is another distinction between it and serum 

 albumin. 



Lactoglobulin. A trace of globulin is obtained from cows' milk by 

 saturating it with magnesium sulphate, after the removal of the 

 caseinogen by saturation with sodium chloride (Sebelien). Its 

 characters are like those of serum globulin. The amount of globulin in 

 colostrum is considerable, but in fully-formed milk it is present in so small 

 an amount that for a long time I was unable to confirm Sebelien's state- 

 ment. Hewlett, 6 however, who worked with me, confirmed its presence. 



1 Ungar. Arch. f. Med., Wiesbaden, Bd. i. S. 192 ; Jahresb. il. d. Fortschr. d. Thier- 

 C/iem., Wiesbaden, Bd. xxii. S. 168. 



2 Inaug. Diss., Bern, 1894. See also Moraczewski, Ztschr. f. physiol. Chem., Strassburg, 

 1894, Bd. xx. S. 28. 



3 Arch.f. d. ges. Physiol., Bonn, Bd. Ivi. S. 558. 



4 Ztschr. f. physiol. Chem., Strassburg, 1897, Bd. xxii. S. 575. 



5 Sebelien, Jahresb. il. d. Fortschr. d. Thier-Chem., Wiesbaden, Bd. xv. S. 184. 



6 Journ. Physiol., Cambridge and London, 1892, vol. xiii. p. 7!>8. See also Arthus, Arch, 

 de physiol. norm, etpath., Paris, 1893, p. 673, 



