222 Kiihne and Chittenden— Peptones. 
tion that pepsin digestions yield leucin and tyrosin, rests wholly 
upon this circumstance, for since the digestion of the mucous mem- 
brane always commences with the disappearance of a mucilaginous 
substance, the derivatives of the latter must necessarily be expected 
in the resultant solution. Probably for this reason, artificial gastric 
juice which has been prepared from mucous membrane and is no 
longer mucilaginous, gives a precipitate when treated with alcohol 
which differs much from the precipitates of albumose and peptone in 
being almost as elastic as rubber and, as a rule, forming when shaken, 
a single ball in which the pepsin is then ordinarily inclosed. We 
have not yet examined this substance closely, since in the course of 
the investigations to be described, another more suitable method for 
precipitating and isolating the ferment has been discovered. We 
shall designate this elastic body for convenience, mucin-peptone. 
This mucin-peptone might possibly conceal the whole amount of pep- 
tone expected from the digested fibrin, or remain mixed with the 
latter in considerable quantity. In spite of this objection, which we 
at no time lost sight of, we prepared a quantity of fibrin-peptone 
without attempting to remove or to prevent the mixture in question. 
The observations made by Dr. Pollitzer* in the Physiological Insti- 
tute at Heidelberg, on the influence of pepsin-peptone free from albu- 
 mose on coagulation of the blood, were performed with such ampho- 
peptone, which is not perfectly pure. 
Supported by the following analyses of this peptone in our pre- 
sumption that it was rendered impure by mucin-peptone, we sought a 
process that would exclude this impurity. This was found almost of 
itself after we had noticed that ammonium sulphate invariably 
precipitated from the acid solutions, in addition to albumose, the 
entire quantity of active pepsin. While, therefore, nothing capable 
of digestion with acids could in any way be obtained from the fil- 
trates, an exceedingly active juice was formed by dissolving the pre- 
cipitate in dilute hydrochloric acid. Hereafter, we accordingly pre- 
pared the strong pepsin solution, by simply precipitating large quan- 
tities of very concentrated gastric juice containing 0°5 per cent. 
hydrochloric acid with ammonium sulphate and dissolving the resin- 
ous precipitate, which did not contain an objectionable quantity 
of albumose bodies, in fresh dilute acid. By this means the 
mucin-peptone was gotten rid of, since it could not be precipitated 
by ammonium sulphate and thus a new method was found for prepar- 
ing and isolating pepsin, which we shall enter upon at another time. 
\ * Verhandl. d. Naturhist. med. Verein zu Heidelberg, N. EB. TLE) p. 298; 
