234 Hind. — Studies in Permeability . Ill . 
was made at a partial separation of the colloidal and crystalloidal substances 
in the expressed liquid, by filtering under pressure in Bechold’s ultra- 
filtration apparatus through a 3 per cent, collodion filter. The filtrate 
so obtained would contain the crystalloids, but a large part of the colloids 
would be left behind on the filter. When 1 c.c. of the filtered solution was 
now added to 100 c.c. acid, there was produced a much smaller decrease in 
the hydrogen-ion concentration of the acid ; thus it appears that the 
decrease in hydrogen-ion concentration, produced by the crude expressed 
liquid, is probably due to the action of the colloidal substances in the 
1000 
potato extract. Formic, acetic, and nitric acids w r ere used in these experi- 
ments. The proteins in some of the solution obtained from the potato 
were precipitated by means of colloidal ferric hydroxide, and the solution 
then filtered. 1 c.c. of the filtrate added to 100 c.c. acid produced no effect 
on the hydrogen-ion concentration of the acid. 
As the removal of protein from the solution also removes its power of 
reducing the hydrogen-ion concentration of acid solutions, it suggests that 
the absorbing substances of the living cells may be proteins. It is known 
that proteins react chemically with acids, and will therefore affect their 
hydrogen-ion concentration. 
A solution of peptone in water was therefore prepared, and 1 c.c. of it 
