98 ANTIGENS AND ANTIBODIES 



delicate layer and serves to attract the leukocytes. As I have already 

 pointed out, the tropins can act independently of the presence of 

 complement and are thus of simpler structure than the opsonins proper 

 both those occurring in normal, as well as those found in immune 

 serum. The quantity of these substances which may occur in 

 immune sera is sometimes very considerable and much greater 

 than that found in normal blood ; for, whereas the latter can scarcely 

 be diluted more than fifty times before it loses its specific action, 

 immune serum may at times still call forth phagocytosis when diluted 

 a thousandfold. 



Antiferments. Another group of antibodies are the so-called anti- 

 ferments which are specifically directed against the corresponding 

 ferments. Substances of this order have been observed in the blood 

 serum after immunization with rennin, pepsin, trypsin, tyrosinase, 

 thrombin, urease, lactase, lipase, laccase, etc., the corresponding 

 antiferments being accordingly designated as antitrypsin, antipepsin 

 antirennin, etc. 



The discovery of bodies of this order is especially interesting as 

 it throws some light on the vexed question: Why do the various 

 cells of the body not digest themselves? In former years when the 

 digestive ferments of the stomach and pancreas were the only ones 

 known to occur in the animal body, it was a source of wonder why 

 the corresponding digestive juices did not digest the organs in which 

 they were produced. At the present time when we know that pro- 

 teolytic ferments are present in every cell we may well wonder why 

 the whole body does not digest itself. If leukocytes are removed 

 from the body and suspended in saline or Ringer's fluid, self-digestion 

 begins after a relatively short time and leads to the complete destruc- 

 tion of the cells, even though the access of bacteria be prevented. 

 If, on the other hand, the cells are suspended in normal serum, 

 autodigestion does not occur, and if such serum be tested against 

 a solution of trypsin it can be shown that it possesses marked anti- 

 tryptic properties. The discovery, then, that the antitryptic content 

 of the blood can be materially increased by immunization with tryp- 

 sin, suggests the possibility, at least, that, even normally, antifer- 

 ment production occurs in the animal body and renders the conclu- 

 sion not unwarrantable that these antiferments are essential to the 

 life of the whole organism. 



