CASEIN. 383 



In order to determine with any certainty whether casein exists 

 in an albuminous fluid, we should conduct our experiment in the 

 following manner. The fluid must be boiled for some time, a little 

 hydrochlorate of ammonia having been first added, to effect the 

 separation of the albuminate of soda ; we must then filter it, and 

 ascertain whether sulphate of magnesia or chloride of calcium 

 yields a precipitate without the aid of heat ; if such a precipitate 

 be formed, we remove it by filtration, before boiling the fluid, in 

 order to search for casein. If a precipitate be formed on boiling 

 the fluid thus prepared, the presence of casein must in this case be 

 shown by rennet. 



Acetic acid was formerly almost the only reagent employed in 

 the quantitative determination of casein ; but this acid by no means 

 effects a thorough precipitation of the casein, and when added in 

 excess it often dissolves a very considerable portion ; an observa- 

 tion which formerly led Schiibler to the belief that the milk 

 contained a peculiar substance, to which he gave a special name, 

 zieger.* The best method of analysing milk which has yet been 

 proposed is, unquestionably, that of Haidlen.f On stirring milk 

 with about one-fifth of its weight of finely pulverised gypsum, and 

 heating it to 100, a perfect coagulation ensues, and we obtain on 

 evaporation a brittle, easily pulverisable residue, from which ether 

 and alcohol easily remove the fat, milk-sugar, and most of the 

 salts. The residue is then not pure casein, but the quantity of 

 that ingredient in a state of purity may be easily calculated by 

 determining the quantity of fat, sugar, and salts contained in the 

 milk. 



Physiological Relations. 



Occurrence. Casein occurs, as is well known, in the milk of all 

 the mammalia. 



ClemmJ found 3*37^-, and Fr. Simon, on an average, 3'5, of 

 casein in women's milk ; the latter found 4f in the colostrum, but 

 only 2*15 in the milk six days after delivery. In women's milk 

 of good quality Haidlen|| found 3' If, but in milk of an inferior 

 character only 2' 7$. 



In cows' milk Boussingault^f found the casein to range from 3f 



* [Zieger is, literally, a sort of whey. o. E. D.] 



t Ann. d. Ch. u. Pharm. Bd. 45, S. 273 ff. 



$ Inquis. chem. etc. Getting. 1845. 



Frauenmilch. Berl. 1838. 



|| Ann. d. Ch. u. Pharm. Bd. 45, S. 273 ff. 



IT Ann. de Chim. et de Phys. 3 Ser. T. 8, p. &6. 



