INFECTION AND IMMUNITY 5 



is necessary. The anaphylatoxin, therefore, is not 

 identical with Pfeiffer's " endotoxins," though per- 

 haps the latter may be the mother substance from 

 which the anaphylatoxin is derived. 



Another important factor in pathogenesis, accord- 

 ing to Bail, is the ability of many bacteria to pro- 

 duce certain neutralizing substances, not directly 

 injurious, but able to inhibit or neutralize the anti- 

 bacterial activities of the body. These substances 

 Bail calls aggressins. There is still some doubt 

 whether they are a distinct class of bacterial 

 products. Wassermann and Citron, Doerr, and 

 others regard them as consisting of dissolved 

 bacterial substances, extracted endotoxins and 

 toxins. 



Resistance Against Infection. The ability of 

 an animal to resist the effects of a pathogenic 

 organism is spoken of as immunity, and may be 

 either natural or acquired. For example, it is well 

 known that the lower animals are immune against 

 syphilis and gonorrhoea, that dogs and goats are 

 rarely affected with tuberculosis, and that man is 

 naturally immune against chicken cholera and 

 rinderpest. These are instances of natural im- 

 munity. Furthermore, it is well established that 

 with certain diseases one attack usually protects 

 the individual for life. This is well seen in 

 small-pox, scarlet fever, and measles. Inasmuch 

 as the individual was previously susceptiW? 



