384 PROTEIN-COMPOUNDS. 



to 3'4, Playfair determined the average at 4*16^, Poggiale* at 

 3'8%, and Simon at f%. 



In the milk of bitches Simon found 14*6$ of casein, Dumasf 

 from 9'73 to 13'6, and BenschJ from 8'34f to W'24% (including 

 the insoluble salts.) In asses 5 milk Peligot found 1*95^ and Stiptr. 

 Luiscius and Bondt|| 2'3&; the latter found 16'2% in mares' milk; 

 in goats' milk, Payen found 4.52-J, Stiptr. Luiscius and Bondt 

 9'1 2, and Clemm 6'03% ; Schlossberger** found 9'66 in the 

 milk of a he-goat, and Stiptr. Luiscius and Bondt 15 '3 in ewes' 

 milk 



According to Dumas and Bensch the milk contains more casein 

 during an animal than during a strictly vegetable diet. 



The nitrogenous substance to which we apply the name of 

 casein, occurs in the milk, for the most part, in a state of solution, 

 but a not inconsiderable portion forms the free investing mem- 

 brane or wall of the milk-globules. The microscope alone affords 

 us no information regarding the structure of this membrane ; hence 

 we do not attach much faith to the assertions of Raspail and 

 Donne,tt wn were the first to assume the existence of such a 

 membrane: Simon{{ believed that he had detected fragments of 

 these membranes in milk which had been evaporated and treated 

 \vith ether; Henle was the first to demonstrate its existence ; on 

 examining under the microscope the gradual action of acetic acid on 

 the milk-globules, he noticed a decided distortion of this membrane. 

 The best proof of the existence of an investing membrane is, how- 

 ever, afforded by an experiment instituted by E. Mitscherlich : on 

 shaking perfectly/res^ milk with ether, it is scarcely at all changed, 

 the ether merely taking up a little fat ; now, if the milk were a 

 simple emulsion, it would yield all its fat to the ether, and would be 

 converted into a transparent, tolerably clear fluid ; as this is not 

 the case, the separate fat-vesicles must be surrounded by an insolu- 

 ble substance; if now we add a substance capable of dissolving these 

 membranes, ether when shaken with milk will act on it precisely 

 as on an emulsion, that is to say, it will take up the fatty matter ; 



* Compt. rend. T. 18, pp. 506-507. 



t Ibid. Bd. 21,8.708-717. 



$ Ann. d. Ch. u. Pharm. Bd. 61, S. 221-227. 



Ann. de Chim. et de Phys. T. 62, p. 432. 



II Me'moires de la Soc. de Me'd. de Paris. 1787, p. 525. 



** Ann. d. Ch. u. Pharm. Bd. 51, S. 431. 



ft Cours de Microscopie, p. 356. 



Et Medic. Chem. Bd. 2, S. 75, or English Translation, vol. 2, p. 43. 



Fror. Notiz. 1839, Nr. 223, and Allgemeine Anatomic, S. 942. 



