ANTI-ENZYME IMMUNITY 181 



Among others, the following may be mentioned: The presence of 

 enzyme inhibitors (or anti-enzymes) in the living cells; the presence 

 of passive or active protective membranes; selective impermeability 

 of the cell membranes to the proteolytic enzymes; the existence of re- 

 pulsive forces between the cell membrane and the proteolytic en- 

 zymes, etc. After a critical analysis of these hypotheses Fermi (1910) 

 rejected them and arrived at the conclusion that the resistance of 

 "living" proteins is due to a difference of "biochemical constitution" 

 between the proteins of living and dead cells. Northrop (1926, 1939) 

 stated that he confirmed the conclusion of Fermi. Of the above hy- 

 potheses, the impermeability of the living and the permeability of the 

 dead cells to proteolytic enzymes appears to have been one of the 

 most important aspects. Northrop stated that "in every case that 

 as long as the cell was alive, no detectable quantity of enzyme was 

 taken up; whereas when the cell dies, the enzyme was rapidly removed 

 from solution and concentrated in the cell." 



In the opinion of Northrop the digestion of heat-killed organisms 

 may be accounted for by assuming a change in the chemical nature of 

 the proteins, or the destruction of the anti-enzymes. These objections 

 cannot, however, account for the digestion of the organisms (earth- 

 worm and mealworm) when killed simply by mechanical injury. It is 

 known that there is an inhibitor in organisms such as the earthworm 

 (Luvtbricus terrestris). The presence of this inhibitor might be consid- 

 ered as the reason for the resistance of the living earthworm to the 

 action of trypsin. This can, however, be ruled out in view of the fact 

 that in the presence of an amount of trypsin in excess of the amount 

 required to neutralize this inhibitor the tissue of the earthworm killed 

 by cutting is found to be digestible (Northrop, 1926). 



In the light of what has been said above, the delayed action of tryp- 

 sin or raw egg albumin in Bayliss' experiment does not appear to be 

 due to an inactivation by adsorption. The gradual "reversal of ac- 

 tivity" beginning with the tenth hour of the reaction period, as de- 

 scribed by Bayliss, and that at the end of the 70th hour, the activity 

 of trypsin on raw egg albumin and on egg albumin denatured at 

 IOO°C. was equal, may indicate a gradual denaturation of raw egg 

 white by dilution with nine volumes of water and standing in contact 

 with the reaction system for such a long time. The denaturation of 



