370 INFECTION AND IMMUNITY. 



quantity injected. 5. The degree of affinity be- 

 tween toxin and antitoxin. 6. The degree of affinity 

 between toxin and tissue cells. 7. The amount of 

 toxin which may be bound without a fatal issue, of 

 which the vital importance of the organs involved 

 and their recuperative powers are factors. 8. The 

 location of the toxin in the body, i. e., its accessi- 

 bility for the antitoxin. 



prophylactic What has been said relates to the curative ac- 

 Antitoxin. tion of antitoxin. It is evident that the action of 

 antitoxin, when used as a prophylactic, is of a 

 simpler nature, for in this instance the conditions 

 approximate those of the test-tube experiment. 

 There has been opportunity for the antitoxin to 

 become uniformly distributed in the blood and 

 lymphatic circulations; hence, it is able to meet 

 and to bind the toxin before the latter comes in 

 contact with the receptors of important cells. The 

 high value of tetanus antitoxin as a prophylactic, 

 a value which has become evident in recent years, 

 probably depends on this condition. 



The immunity which is afforded by a prophy- 

 lactic injection of antitoxin is of short duration, 

 from two to three weeks; the antitoxin is excreted 

 in the urine to a considerable extent, but in part 

 may be bound and assimilated by the tissues. 



(B) BACTERICIDAL OR ANTIBACTERIAL SERUMS. 



Bactericidal Attention has been directed repeatedly to a 

 large group of organisms the toxic constituents of 

 which are integrally associated with the proto- 

 plasm of the microbes; the toxic substances are 

 endotoxins. Certain members of this group, of 

 which the typhoid, paratyphoid, colon and dysen- 

 tery bacilli and the vibrio of cholera are represent- 



