108 PATHOGENIC BACTERIA. 



Alessi, 1 in investigating this subject, confined rats, 

 rabbits, and guinea-pigs in cages, some of which were 

 placed over the opening of a privy, while in others the 

 excreta of the animals was allowed to accumulate in a 

 receptacle below. The inhalation of the vapors from the 

 excreta caused so marked a difference in the resisting 

 powers of the animals that, while the control animals all 

 resisted it successfully, the rats succumbed to an injec- 

 tion of the typhoid fever bacillus in from twelve to thirty- 

 six hours after from five to seventy-two days' exposure to 

 the vapors ; guinea-pigs after seven to fifty-eight days ; 

 and rabbits after three to eighteen days' exposure. 



Abbott, 2 on the contrary, forced rabbits for as long as 

 one hundred and twenty-nine days to breathe air which 

 had been passed through sewage or through putrid meat 

 infusions. He concludes that "the products of decom- 

 position . . . play no part in either producing diseased 

 conditions or in inducing susceptibility to infection." 



c. Fatigue has marked influence in reducing immunity, 

 the fact being well recognized clinically. Charrin and 

 Roger 3 found that the white rat, which usually resists 

 inoculation with anthrax, becomes infected and dies if 

 compelled, before inoculation, to turn a revolving wheel 

 until exhausted. 



d. Exposure to cold is viewed by clinicians as one of 

 the most fruitful sources of reduction of immunity, and 

 the occurrence of most of the infectious diseases not other- 

 wise explained is referred to it. This is not without 

 reason, for its influence upon pneumonia, bronchitis, etc. 

 can scarcely be doubted. Experimentally, its influence 

 has been shown in the classic experiment of Pasteur, 

 who found that fowls that naturally resist anthrax become 

 susceptible if given a cold bath before inoculation. 



e. Peculiarities of diet may reduce immunity. Hankin 

 observed that the immunity of rats to anthrax was in 



1 See abstract in the Centralbl. f. Bakt. u. Parasitenk., 1894, xv., 228. 

 1 Transactions of the Association of American Physicians, 1895. 

 8 Compte-rendu Soc. de Biol, de Paris, Jan. 24, 1890. 



