: Primary Cleavage Products. 379 
amount in the acetic acid precipitate being fully as large as in the 
casein precipitated by hydrochloric acid. 
Compared with Ritthausen’s results (see table showing average 
composition), obtained by analysis of the copper compound of casein, 
the percentage of carbon comes very much too high. It is question- 
able, however, how close a comparison should be drawn between 
indirect results obtained by analysis of a metallic compound of 
casein and those obtained by analysis of casein itself. 
In conclusion then, we must affirm that our results accord closely 
with those of Hammarsten’s, while the two together make it very 
improbable that in casein we have to do with a substance composed 
of two bodies of unlike composition. 
Digestion of Casein and Formation of Caseoses. 
In the digestion of casein with pepsin-hydrochloric acid, the casein 
was prepared by precipitation and reprecipitation with acetic acid, 
and rendered as pure as possible by thorough washing with water. 
While still moist it was placed in 0°4 per cent. hydrochloric acid, as 
preliminary to its treatment with pepsin. Pure pepsin solution, free 
from peptone and albumose, was prepared from the mucous mem- 
brane of pig’s stomachs by the method already described.* 
Digestion A. 
1300 grams of moist casein in 4 litres of 0-4 per cent. hydrochloric 
acid were brought to a temperature of 45° C. and 600 cc. of pure 
pepsin solution added. The mixture was kept at a temperature of 
45° C. throughout the digestion. The casein began almost immedi- 
ately to swell up and in less than an hour the entire mixture was con- 
verted into a semi-solid, jelly-like mass. Thereupon, one litre more 
of 04 per cent. hydrochloric acid was added, together with a little 
more pepsin solution. At the end of three hours, the mixture was 
quite fluid, but contained considerable gelatinous matter in suspension. 
Neutralization of a filtered portion, produced no précipitate whatever. 
The addition of crystals of sodium chloride gave a heavy white pre- 
cipitate and the filtrate from this precipitate gave a further precipi- 
tate on the addition of acetic acid. At the end of four hours, the 
entire mixture was made neutral with sodium hydroxide and then 
filtered through paper. The undigested residue, when dry, amounted 
to about 30 or 40 grams. This residue of so-called casein dyspeptone, 
* See the preceding article on egg-albumin and albumoses. 
