124 INFECTION 



organism, an acute and fatal infection followed. Similar results were 

 secured with the bacilli of dysentery, chicken cholera, pneumonia, and 

 other diseases. 



Bail's Classification of Bacteria. Bail found that bacteria differed 

 in their power of forming aggressins; he therefore used this principle 

 in making a division of bacteria into three classes, according to their 

 disease-producing power, as dependent largely upon whether or not the 

 microorganism can produce an aggressin that is active against the pro- 

 tective forces of the host, particularly against opsonins and leukocytes. 



1. Saprophytes, or those bacteria that, when injected even in large 

 doses, do not produce any characteristic disease. 



2. True parasites, or those bacteria that, when injected even in the 

 smallest amounts, will produce disease and death. These are truly 

 virulent, and the number of bacteria increase so rapidly as to be demon- 

 strable in every drop of blood and in all the organs. Examples of true 

 parasites are the bacilli of anthrax and of chicken cholera, the tubercle 

 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 sjTnptoms, 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 



