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XV.—Peprtronges. By W. Ktune anv R. H. Cuirrenpen. 
Since there has been discovered in neutral ammonium sulphate a 
means for the complete precipitation of the albumose bodies, we 
have been induced to take up anew our former investigations on the 
behavior and composition of peptones. As these latter bodies are 
not precipitated by the ammonium salt, we had expected to obtain 
peptones free from the primary cleavage products of albumin and 
thereby advance another step in our knowledge of the definite prod- 
ucts of the proteolytic action both of pepsin and of trypsin. Re- 
newed investigation was demanded by the probability that hitherto 
pepsin-peptones entirely free from albumose have never been ob- 
tained, for such peptones as are to be found in commerce or in the 
hands of the most careful investigator of gastric digestion can 
readily be shown to contain albumose by saturating a solution of 
the preparation with ammonium sulphate. There will result an 
abundant precipitate of albumose and a surprisingly small residue 
of non-precipitated pep‘ones or the entire absence of such a residue. 
Only antipeptone obtained by trypsin digestion will occasionally 
form an exception, and even then in most cases we cannot but doubt 
that the peptones so formed are wholly free from albumose. 
In order to be certain of the presence of peptones in a digestive 
fluid, it must be made slightly acid with acetic acid, rubbed 
up with ammonium sulphate till saturated and then filtered from 
the excess of salt and the albumose precipitate. If the filtrate 
is thereupon treated with a large excess of strong sodium hydrox- 
ide and then a few drops of very dilute cupric sulphate be added, 
the appearance of the rosy red color of the biuret reaction will — 
indic&te the presence of peptones. If peptones are absent the 
fluid will be pure blue without a tinge of violet, since the solution 
can contain no other albuminous body. Even after an apparently 
energetic pepsin digestion the latter result is not at all rare, and a 
heavy precipitate by the ammonium salt is so frequently seen, that it — 
is still to be doubted whether there is a pepsin-acid digestion which 
causes the disappearance of all albumose, On the contrary, the albu- 
mose precipitate after a sufficiently long and energetic trypsin diges- — 
tion is very slight and peptone is to be found abundantly in the 
solution. 
