INFLUENCE OF TEMPERATURE 449 



which strongly retard protein hydrolysis has been observed by a 

 number of investigators. Thus Schwarz (64) has shown that if 

 solutions of pepsin be heated to 80 degrees for some time and then 

 added to peptic digests the digestion is greatly retarded, while 

 Pollack (46) had previously obtained, by heating pancreas extracts 

 to 70 degrees, a substance which greatly retards tryptic hydrolysis 

 of proteins; he further observed that this substance is a colloid 

 since it does not pass through the membrane of a dialysor. Hensel 

 (29) has observed that if the mucous membrane of a stomach be 

 treated with acidulated water at 50 degrees, the watery extract 

 thus obtained contains an organic substance which greatly retards 

 peptic hydrolysis of proteins. Beam and Cramer (6) have found 

 that solutions of rennet which have been heated to from 56 to 

 60 degrees exert an inhibitory influence on the activity of unheated 

 rennet. Bayliss (4) has found that heated trypsin not only greatly 

 delays the tryptic hydrolysis of casein but would appear to in- 

 augurate a chemical reaction in the reverse sense, since mixtures 

 of heated trypsin and a caseinate, instead of increasing in conduc- 

 tivity with time, at first decrease in conductivity, later slowly 

 increasing. Similar phenomena have been observed with other 

 enzymes (15) (6). 



The anti-tryptic actions of such substances as egg-white (72) (4), 

 normal blood serum (22) (17) (49) (37) (12) (24) and extracts of 

 intestinal worms (13) and the anti-peptic and anti-tryptic actions 

 of the bodies produced in the circulation by the injection of pepsin 

 and trypsin into living animals (58) (1) (74) have usually been 

 attributed to the formation of more or less stable compounds 

 between the ferment and the anti-ferment. One would be in- 

 clined to similarly attribute the action of heated solutions of pepsin 

 and trypsin in inhibiting these ferments to the formation of com- 

 pounds between the heated and the normal ferment were it not 

 that the heated ferment, although deprived of its power to acceler- 

 ate hydrolysis of protein, markedly accelerates its synthesis. The 

 inhibitory action of the heated ferment is thus clearly seen to 

 consist in bringing about a change which is opposite in sense to 

 that which is brought about by the normal ferment.* We see, 



* Bayliss, regarding the phenomenon from the standpoint of EhrUch's 

 "side-chain" hypothesis, has advanced the opinion that the decrease in con- 

 'ductivity which is observed upon the addition of heated ferment to a solu- 

 tion of protein is to be attributed to the destruction of the "zymophore," or 



