126 INFECTION 



bacillus for guinea-pigs, and the bacilli of the group of hemorrhagic 

 septicemia for rabbits. 



3. Half or partial parasites are those bacteria the infectious nature 

 of which depends upon the number of bacteria injected. The smaller 

 the number, the milder the symptoms, until a dose is reached below 

 which no disturbances are produced. Organisms of this class possess 

 some virulence and toxicity, examples being the Bacillus typhosus and 

 the Spirillum cholerae. 



It is to be remembered, however, that these effects are but relative, 

 and dependent upon the organism, the species of animal, and the mode of 

 infection. For example, the bacillus of anthrax is saprophytic for the 

 frog and hen unless the temperature of these animals is brought to the 

 body temperature of the human; a bacillus of the group of hemorrhagic 

 septicemia of rabbits is saprophytic for human beings, a half parasite 

 for the guinea-pig if injected subcutaneously, and a true parasite for the 

 same animal if injected intraperitoneally. 



Nature of Aggressins. The aggressins in inflammatory exudates 

 are presumably substances capable of paralyzing the protective agencies 

 of the body. Bail regards the aggressins as of the nature of endotoxins 

 liberated from the bacteria as a result of bacteriolysis, and believes that 

 they act by paralyzing the polynuclear leukocytes, thereby preventing 

 phagocytosis. In general, the production of these aggressins goes on 

 more actively the greater the resistance to the bacteria; they are pro- 

 duced in greater quantities during the struggle between the bacteria and 

 the body-cells, although they may be produced artificially in the test- 

 tube with large numbers of bacteria and a non-poisonous agent (serum 

 or distilled water) which can disintegrate the cells. In this manner 

 Wassermann and Citron have produced "artificial aggressins, " which act 

 in the same general manner as the "natural aggressins" of Bail. 



By many the aggressins are regarded as endotoxins, and while they 

 may possess the nature of endotoxic substances, it is to be remembered 

 that there is no definite relation between the poisonous qualities of the 

 aggressins and their power to increase the virulence of an infection. It 

 is probable, as has been shown by Wassermann and Citron, that patho- 

 genic bacteria contain small amounts of natural aggressin. This ag- 

 gressin may be regarded as a normal antibody of the bacterium against 

 the defensive forces of the body-cells of a host. During infection these 

 aggressins or antibodies are naturally greatly increased, as the bacteria 

 require more and more protection. Being contained to some extent 

 within the bacterial cells, the antibodies are somewhat similar to endo- 

 toxins: while endotoxins may be regarded as offensive agents of bacte- 



