BIOLOGY OF CLOSTRIDIUM WELCHII 421 



XII. IMMUNITY 



In the literature dealing with the immunity of animals to 

 inoculation with Clostridium Welchii and the production of im- 

 mune sera, we find views as varied and unreliable as in regard 

 to the other properties of this organism. Very little work has 

 been done on the production of artificial immunity. Previous 

 to 1916, investigators were unable to protect guinea-pigs against 

 infection by injections of bacilli killed either by heat or by chemi- 

 cal substances. A pig which had recovered from one inoculation 

 was believed to be more susceptible to a new injection. 



On the other hand Rosenthal and Theroloix, 1909, immunized 

 horses against Cldstridium Welchii and produced a serum which 

 protected rabbits against intrapleural and intramuscular injec- 

 tions of the living organisms. These results were not in line with 

 other observations made at that time yet later evidence seems 

 to justify their validity. 



Robertson, 1916, undertook experiments to determine whether 

 or not immunity could be produced by the prophylactic inocu- 

 lation of Clostridium Welchii and his results showed no immunity 

 in guinea-pigs, and also indicated that the survival of one infection 

 did not confer any immunity at a later period. 



As far as is known Bull and Pritchett, 1917, are the only ones 

 who have shown that the toxic products of Clostridium Welchii 

 exhibit antigenic activities and give rise to the formation of 

 active antitoxic substances which possess protective and curative 

 properties. Conclusions from their work show that animals may 

 be immunized actively so as to yield an immune serum which 

 neutralizes the toxin perfectly and in multiple proportion. 



As stated, different strains vary greatly in virulence and the 

 same strain varies according to cultural conditions. The con- 

 ditions under which five experiments were performed to produce 

 immunity were not sufficiently controlled to render conclusive 

 evidence; in particular, too much time elapsed between inocula- 

 tions. With all the conditions controlled and standardized, it 

 is believed however that a lasting immunity can be produced 

 for guinea-pigs. A description of the five experiments follow: 



