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. 
Ringer'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 use 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-albuiiiin. 
Analyses by Chittenden 1 gave the following result — C, 53 - 3 : H, 7 - 07 ; 
N", 1591; S. 0-82; 0, 22-04. The amount of phosphorus was not 
estimated. Danilewsky- 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 l - 3 to 211 per cent. 
of the caseinogen employed ; he finds that the amount of phos- 
phorus in the pseudo-nuclein varies from 0-88 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 Halm. 10 These ol >sei vers also find that 
1 Stud. Lai}. Physiol. Chem., New Haven, vol. ii. p. 156 ; iii. p. 66. 
2 Ztschr. f. physiol. Chan.. Strassburg, Bd. vii. S. 433. 
3 Ibid., Bd. vii. S. 227. 
4 On peptonised milk see also Horton-Smith. Journ. Physiol., Cambridge and London, 
1891, vol. xii. p. 42. 
5 Central I . Chem., Leipzig. 1889, S. 717. 
6 Moraczewski, Ztschr. f. physiol. Chem., Strassburg, Bd. xx. 
7 Loc. cit. s xoc. cit. 
9 Ztschr. f. physiol. Chen., Strassburg. 1894, Bd. xx. S. 28. 
10 Arch. f. d. gcs. Physiol., Bonn, Bd. lix. 
