G2 
FIFTEENTH REPORT. 
about two hours. The results of our experiment with heated saliva are 
as follows. Three specimens were each boiled for one minute; 2 of 
these were reactivated in 1 hour and 40 minutes; the third remained 
inactive. Four specimens were boiled for 2 minutes;- two of these were 
reactivated in 1 hour and 20 minutes; one in 2 hours; and the fourth 
not at all. Five specimens were boiled for 4 minutes; one of these was. 
partially reactivated in 2 hours and 30 minutes; none of the remaining 
four became active. Of five specimens boiled for five minutes none were 
reactivated by dialysis. 
This inactivation by heat is not to be considered entirely as an actual 
destruction of the ferment, but rather due to the products of cleavage 
of the other components of the complex colloidal system of which the 
ferment forms only a part. Heat applied to a protein solution causes 
a cleavage of the protein molecule with the liberation of neutral salts, 
free alkali, and amino-acids. The addition of these products to any 
bio chemical system markedly retards or entirely prevents its progress. 
If, however, they are removed by dialysis the system can in a few in- 
stances be reactivated. 
It sometimes happens that one of the products of the reaction acts 
catalvtically on the reaction. This is known as autocatalysis. It is 
common to metals which dissolve in acids. For instance, the action is 
slow when copper is added to pure nitric acid. Nitrous acid is a 
product of the reaction, and this acting catalvtically greatly increases 
the velocity. Thus, this reaction increases in velocity as it proceeds. 
The characteristic course of a reaction involving autocatalysis is a 
velocity, small at first, ascending to a. maximum, then descending. What 
we at first thought to be a typical example of autocatalvsis is outlined 
in the following experiment. Cubes of egg-white and pepsin hydro-cliloric 
acid were placed within a collodion sac, outside of the sac were hydro- 
chloric acid of the same strength and egg-white cubes. This was set aside 
for a time at 38°C. There was almost complete digestion within the 
sac after an incubation of 35 hours, and the egg-white in the outside 
fluid was partially digested. Assuming that the pepsin could not 
pass through the sac we explained the digestion of the outside egg-white 
bv the assumption that the dialyzed products of digestion exerted typical 
autocatalysis. Control experiments, however, showed that the pepsin 
was dialyzable through the membrane. The same findings were dupli- 
cated with ptyalin and starch, also with rennet and milk. These fer- 
ments are, then, diffusable through eolodion sacs, in fact almost as 
readily so as are their products of cleavage. 
That the associated components in a ferment mixture influence the 
dialysis of a ferment is shown in the following experiment: We find 
that if saliva is placed within a collodion sac and this surrounded by a 
soluble starch solution, glucose does not appear in the starch solution 
for at least 45 minutes after the beginning of the experiment. If, first, 
the saliva is filtered through Kieselguhr or a Berkefeld filter, which 
process if repeated several times does not appreciably lessen the ferment 
content, the enzyme dialyzes very quickly into the starch solution; the 
simple sugars appeared within 5 minutes in three experiments out of 
seven. Why should the ferment of the filtered saliva dialyze more 
rapidly than that of the unfiltered? All colloids are more or levss ad- 
sorbed by surfaces, and in these experiments the membrane must become 
