628 MILK. 



dissolves completely and easily in an excess of juice; the casein precipi- 

 tate produced by an acid is more easily soluble in an excess of the acid ; 

 and lastly, the clot formed from the casein of woman's milk does not 

 appear in such large and coarse masses as in the casein from cow's 

 milk, but is more loose and flocculent. This last-mentioned fact is of 

 great importance, since it explains the generally admitted fact of the 

 easy digestibility of the casein from woman's milk. We are not clear 

 as to this difference between the digestibility of the cow's casein and 

 human casein, as the first seems to be utilized in the intestinal tract of 

 the infant to the same extent as human casein (P. MULLER, RUBNER and 

 HEUBNER l ). 



The question as to whether the above-mentioned variations depend 

 on a decided difference in the two caseins or only on an unequal relation 

 between the casein and the salts in the two kinds of milk, or upon other 

 circumstances, has not been decided as yet. According to SZONTAGH 

 and ZAITSCHEK and also WROBLEWSKY, the casein from human milk 

 does not yield any pseudonuclein on peptic digestion, and hence it cannot 

 be a nucleoalbumin. WROBLEWSKY found the following for the com- 

 position of casein from woman's milk: C 52.24, H 7.32, N 14.97, P 0.68, 

 S 1.117 per cent. LANGSTEIN and BERGELL obtained much lower 

 figures for N, S and especially P, namely, 14.34, 0.85 and 0.27 per cent 

 respectively. According to KOBRAK 2 woman's casein yields some pseu- 

 donuclein, and with repeated solution in alkali and precipitation by an 

 acid it becomes more and more like cow's casein. He therefore suggests 

 the possibility that woman's casein is a compound between a nucleo- 

 albumin and a basic protein. 



Woman's milk also contains lactalbumin, besides the casein, and a protein 

 substance, very rich in sulphur (4.7 per cent) and relatively poor in carbon, which 

 WROBLEWSKY calls opalisin. The statements as to the occurrence of proteoses and 

 peptones are conflicting as in many other cases. No positive proof as to the 

 occurrence of proteoses and peptones in fresh milk has been given. 



Because of the properties and low amount of casein in human milk 

 it is often difficult to precipitate it with acid and to prepare it, but 

 this can easily be accomplished by dialysis. A number of methods 

 have been suggested for the preparation of human casein. FULD 

 and WOHLGEMUTH recommend the freezing of the milk previous to 

 precipitation, so that the casein masses become larger to a certain extent 

 and the precipitation becomes easier. ENGEL 3 recommends dilution with 



1 Miiller, Zeitschr. f. Biologie, 39; Rubner and Heubner, ibid., 37. 



2 Szontagh, Maly's Jahresber., 22; Zaitschek, 1. c.; Wroblewsky, Beitrage zur 

 Kenntniss des Frauenkaseins, Inaug.-Diss. Bern, 1894, and Ein neuer eiweissartiger 

 Bestandteil der Milch, Anzeiger der Akad. d. Wiss. in Krakau, 1898; Kobrak, 

 Pfliiger's Arch., 80; Langstein and Bergell, cited in Bioch. Centrabl., 8, 323. 



3 Fuld and Wohlgemuth, Bioch. Zeitschr., 5; Engel, ibid., 14. 



