136 THE CHEMISTRY OF THE TISSUES AND ORGANS. 



salt, and then distilled water is added. This, in virtue of the salt adhering 

 to the precipitate, dissolves out the caseinogen, and carries it through 

 the filter, the greater part of the fat being left behind. From this 

 solution the caseinogen is precipitated by acetic acid ; it is collected, 

 thoroughly washed, and dissolved in dilute alkali like lime water, and 

 purified by repeated precipitation with acid and re-solution in alkali. 



Einger's method of obtaining caseinogen is a slight modification of 

 that of Hammarsten : he precipitates caseinogen with acetic acid, collects 

 and washes the precipitate, and grinds it up in a mortar with calcium 

 carbonate ; the mixture is thrown into excess of distilled water ; the fat 

 rises to the top; the chalk falls to the bottom, and the intermediate 

 opalescent fluid is a solution of caseinogen. The separation into the 

 three layers may be hastened by the ne of the centrifuge. 



In both cases, the caseinogen, if it has been thoroughly washed from 

 soluble calcium salts, will not clot with rennet ; the lime water in the one 

 case and the calcium carbonate in the other not being sufficient to 

 cause the separation of the curd : this, however, occurs immediately on 

 the addition of a soluble salt of lime like the phosphate or chloride. 



Solutions of caseinogen are not coagulated by heat. By prolonged 

 heating they become opalescent ; this often disappears on cooling. In 

 some cases a scum forms on the surface, as in milk. 



Caseinogen is not a globulin ; still less is it an alkali albumin : it is 

 a nucleo -albumin. 



Analyses by Chittenden l gave the following result C, 53*3 ; H, 7'07 ; 

 N, 15-91; S, 0-82; 0, 22'04. The amount of phosphorus was not 

 estimated. Danilewsky 2 considered it to be a mixture of two proteids, 

 but this, as Hammarsten 3 showed, was due to faulty methods of prepara- 

 tion. Chittenden made a study of the caseoses and proteoses obtainable 

 from it by digestion. 4 Sebelien, 5 who also prepared casein peptone, 

 states it is optically inactive a most exceptional occurrence among pro- 

 teids. The most interesting fact about its digestion by gastric juice, 

 however, is, that it yields a precipitate of nuclein, or rather of pseudo- 

 nuclein 6 (see pp. 65, 66). 



The amount of and varieties of calcium phosphate in union with 

 caseinogen and casein has been investigated by Soxhlet and Soldner 7 

 and by Courant. 8 Soldner describes two calcium compounds of 

 caseinogen, containing respectively T55 and 2*36 per cent, of CaO ; these 

 are called dicalcium casein and tricalcium casein. Moraczewski 9 finds 

 that the yield of pseudo-nuclein varies from 1*3 to 21*1 per cent, 

 of the caseinogen employed; he finds that the amount of phos- 

 phorus in the pseudo-nuclein varies from O'SS to 6 - 86 per cent. The 

 whole phosphorus of the casein is not in the nuclein ; the quantity 

 in the nuclein is given as from 6 to 60 per cent, of the whole. This has 

 been confirmed by Salkowski and Hahn. 10 These observers also find that 



1 Stud. Lab. Physiol. Chem., New Haven, vol. ii. p. 156 ; iii. p. 66. 



2 Ztschr. f. pJiysiol. Chem., Strassburg, Bd. vii. S. 433. 

 * Ibid., Bd. vii. S. 227. 



4 On peptonised milk see also Horton-Smith, Journ. Physiol., Cambridge and London, 

 1891, vol. xii. p. 42. 



5 Centralbl.f. agric. Chem., Leipzig, 1889, S. 717. 



6 Moraczewski, Ztschr. f. physiol. Chem., Strassburg, Bd. xx. 



7 Loc. cit. 8 Loc. cit. 

 9 Ztschr. f. physiol. Chem., Strassburg, 1894, Bd. xx. S. 28. 



10 Arc.h.f. d. ges. Physiol., Bonn, Bd. lix. 



