226 Kithne and Chittenden— Pep tones. 
small amount of albumose bodies, while a portion digested as a test 
for the third time, gave in the filtrate from the precipitate produced 
by the ammonium salt, so faint a biuret reaction for peptones that it 
was plainly evident, that the slight residue of albumins from the 
mucous membrane now remaining, could be overlooked without 
danger. 
Digestion of the jfibrin.—3800 grams of washed but not boiled 
fibrin were digested with the twice precipitated pepsin, which 
was dissolved in ten litres of 0-4 per cent. hydrochloric acid. To 
obtain as little albumose and as much peptone as possible, the mix- 
ture was allowed to remain at 37°-40° C. for two weeks. At the end 
of that time, filtered portions gave only slight precipitations by neu- 
tralization, but a heavy precipitate was obtained with ammonium 
sulphate, with sodium chloride, with sodium chloride and acetic acid, 
and still further by sodium chloride and nitric acid or metaphos- 
phoric acid. Nevertheless the filtrate saturated with ammonium 
sulphate contained much peptone.* 
Preparation and purification of the peptone.—For this purpose the 
filtrate was neutralized with sodium hydroxide, filtered through 
linen, especially for removing the impurities of the fibrin, the filtrate 
slightly acidified with acetic acid, concentrated to about four litres, 
precipitated with an excess of ammonium sulphate, filtered and 
pressed, the solution boiled with barium hydroxide and finally with 
barium carbonate and a large quantity of water, until ammonia could 
no longer be detected. The barium sulphate was then removed by 
filtration through cloth bags which were repeatedly washed and 
pressed, the solution evaporated to about four litres, the barium- 
peptone decomposed with a very slight excess of sulphuric acid, the 
new precipitate of barium sulphate filtered off, the solution concen- 
trated to two litres, the free acid neutralized with ammonia and after 
cooling, six per cent. English sulphuric acid (previously diluted) 
was added; then the sulphuric acid-peptone solution was precipitated 
with a large excess of phosphotungstic acid, the precipitate washed 
first with six per cent. sulphuric acid, then with a large quantity of | 
water, after which the compound was decomposed with excess of 
barium hydroxide and the excess completely removed from the fil- 
*Later experiments have shown that pepsin acts much more energetically if the 
ammonium sulphate is completely removed by dialysis, before each new solution and 
digestion of the pepsin-containing precipitate in hydrochloric acid, and further, that 
nearly pure pepsin becomes wholly inactive by being warmed with dilute hydrochloric 
acid iu the presence of even small quantities of ammonium sulphate. 
