New YorkK AGRICULTURAL EXPERIMENT STATION. 195 
of casein, we are largely in the dark, except in the case of 
some of the simpler ones. In the second place, this field is 
difficult to study, because the quantities of individual com- 
pounds that we have to work with are usually very small. 
Under these conditions, methods of quantitative separation 
must, at best, be regarded as largely empirical and more or 
less tentative. Instead of estimating individual compounds, 
about which our chemical knowledge is complete, we are com- 
pelled, in a large degree, to estimate groups of compounds, the 
individual members of which we know, for the most part, in- 
completely, or not at all. 
From the peptic digestion of casein, Chittenden has separated 
the proto- and deutero-caseoses,* and, from a tryptic digestion, 
a deutero-caseose and a peptone.2 Alexander® has separated 
hetero-caseose from a peptic digestion of casein, but only in 
small quantities. Many investigators have observed paranuclein 
or pseudonuclein, the insoluble residue remaining from the 
peptic digestion of casein or paracasein. Emil Fischer and 
P. A. Lavene! have obtained pyrrolidine-a-carbonic acid from a 
tryptic digestion of casein. 
By hydrolysis of casein with hydrochloric acid, Cohn? ob- 
tained l-parahydroxyphenyl-4-amidopropionic acid (tyrosine), 
l-ac-amidoisobutylacetic acid (leucine), amidosuccinic (aspartic) 
acid, ¢-amidoglutaric (glutamic) acid, a pyridine derivative, and 
ammonia; by the same means, Emil Fischer® has recently iso- 
lated, among the monoamido acids, in addition to products pre- 
viously obtained by others, amidovaleric acid, phenyl-a-amido- 
propionic acid (phenylalanine), pyrrolidine-?-carbonic acid, and 
probably amido-acetic acid (glycocoll). 
Among the crystallizable end-products which have been found 
in ripening cheese are the following: Tyrosine, leucine, histi- 
dine, a, -diamidocaproic acid (lysine), tetramethylenediamine (pu- 
trescine), pentamethylenediamine (cadaverine), lysatine, guani- 
dine probably, and ammonia. Most of these products have been 

1Studies in Physiol. Chem. Yale Univ., 2: 156 (1884-5). 
2Studies in Physiol. Chem. Yale Univ., 3: 66 (1887-8). 
3Zeit. f. Physiol. Chem., 25: 411 (1898). 
4Zeit. 7. Physiol. Chem., 33: 170 (1901). 
5 Ber. deut. Chem. Ges., 29: 1785 (1896). 
6Zeit. —. Physiol. Chem., 33: 151 (1901). 

