140 THE CHEMISTRY OF THE TISSUES AND ORGANS. 
Kemmerich l stated that casein (i.e. caseinogen) is formed at the cost of 
the albumin of milk after secretion. He estimated the caseinogen by pre- 
cipitating it with dilute acetic acid, the precipitate being subsequently freed 
from fat by etber, dried and weighed. He estimated the albumin by weighing 
the heat coagulum after separating out the acetic acid precipitate, and he found 
that, after tbe milk is allowed to stand some hours at the body temperature, 
the caseinogen increases in quantity, and the albumin diminishes. Dahnhardt 2 
claimed to have separated out from the cells of the mammary gland a ferment 
soluble in glycerine which hastens this process. 3 
These experiments are quoted with approval by Heidenhain, 4 but do not 
seem to have been followed up recently by the more precise methods of 
modern milk analysis. The differences noted by Kemmerich are usually small, 
and might be well within the limits of experimental error. 5 They date from a 
time when lact-albumin was considered to be identical with serum-albumin, 
and when caseinogen was looked upon as nothing more than alkali-albumin. 
Among other statements made by Kemmerich is the one that lact-albumin is 
converted into casein by boiling — an assertion which is quite sufficient to show 
the somewhat crude notions prevalent at the time concerning the proteids of 
milk. The dominant idea of these workers appears to be to account for the 
milk-proteids as simple derivatives of the blood proteids. 
In the foregoing account of milk, no description of analytical processes bas 
been given. For the numerous methods which may be used in this highly 
technical branch of analytical chemistry, the reader is referred to text-books 
on that science. 
1 Arch. f. J. ges. Physiol., Bonn, 1869, Bd. ii. S. 401. 
*Ibid., 1870, Bd. iff. S. 586. 
s J. C. Lehmann considered that caseinogen is formed from albumin by weak alkali 
(Centralbl. f. d. med. Wissensch., Berlin, 1864, S. 530). 
4 Hermann's " Handbuch," 1883, Bd. v. S. 395. 
5 That this explanation is probably correct, is shown by some experiments of Schmidt- 
Miilheim {Arch.f. d. ges. Physiol., Bonn, 1882, Bd. xxviii. S. 243) and Thierfelder {ibid., 
1883, Bd. xxxii. S. 619), who, by using the same methods, found a slight diminution of the 
casein alter milk had stood some hours at the body temperature. Schmidt-Mulheim sup- 
posed that on standing some of the casein is converted into peptone. 
