ACTION OF THE ENZYMES. 135 



activity markedly. If the ascaris extract is kept at 95 C. 

 for ten minutes, it has lost its protective power altogether. 



At ordinary room temperature ascaris extract keeps very 

 well when 1 to 2 percent of sodium fluoride have been added 

 to it to prevent the development of bacteria. Under these 

 conditions WEINLAND has kept an extract for eight months 

 without apparent loss in the power of the juice to inhibit the 

 action of proteolytic enzymes. 



We have in the foregoing paragraphs spoken of antipro- 

 teinase as though it were a single substance. It is possible 

 that there exist several antiproteinases, though this question 

 is still unsettled. It may be that there exists an antialkali- 

 proteinase (antitrypsin) and an antiacid-proteinase (anti- 

 pepsin), but further experiments must be made to settle this 

 point definitely. 



8. Why the Alimentary Tract Does Not Digest Itself. 

 WEINLAND'S discovery of antiproteinase (antipepsin and anti- 

 trypsin) is of fundamental physiological importance, giving 

 us, as it does, a partial explanation of the immunity which 

 " living " tissues possess towards the proteolytic enzymes. It 

 is a well-known fact, for example, that the intestinal worms 

 nematodes, trematodes, cestodes, etc. are not acted upon 

 by the secretions of the stomach, pancreas, and small intes- 

 tine, which so readily and rapidly bring about the digestion 

 of the ordinary proteins that enter the alimentary tract as 

 food. In the same way we know that cysticerci, the larvae 

 of tapeworms, must pass through the stomach in order to 

 get into the intestine, where they develop into the adult 

 animals. In this passage through the stomach they are sub- 

 jected to the action of the gastric juice; this digests the sac 

 in which the larva is contained, as well as the body of the 

 larva, the head and neck only being able to pass on undigested 

 into the intestine. From these fragments the adult develops, 

 and this in spite of the fact that the growing animal is daily 

 bathed in streams of intestinal contents which are charged 

 with most active proteolytic enzymes. We know that a 



