BACILLUS TYPHOSUS. 417 



question concerning the influence of gaseous products 

 of decomposition upon the health of individuals, and 

 particularly upon the part played by them in diminish- 

 ing natural resistance to infection.' 



Because of the variations in the morphology and cult- 

 ural peculiarities of this organism, and because of the 

 difficulty experienced in efforts to reproduce in lower 

 animals the conditions found in the human subject, 

 typhoid fever is bacteriologically one of the most unsat^ 

 isfactory of the infectious diseases. 



A number of other organisms appear botanically to 

 be closely related to the typhoid bacillus, and with our 

 present methods for studying them they so closely simu- 

 late it that the difficulty of identifying this organism 

 is sometimes very great. In addition the variability 

 constantly seen in pure cultures of the typhoid bacillus 

 itself in no way renders the task more simple. 



For example, the morphology of the typhoid ba- 

 cillus is conspicuously inconstant ; its growth on potato, 

 which was formerly described as characteristic, may, 

 with the same stock, at one time be the typical invis- 

 ible development, at another time it may grow in a way 

 easily to be seen with the naked eye ; and the change of 

 reaction which it is said to produce in bouillon is some- 

 times much more intense than at others. The indol- 

 producing function, hitherto regarded as absent from 

 this organism, is now known to be occasionally de- 

 monstrable by ordinary methods, and frequently by 

 special methods of cultivation. (Peckham, I. c.) The 



• See paper by the author : " The Effects of the Gaseous Products of 

 Decomposition upon the Health, and Kesistance to Infection, of Certain 

 Animals that are Forced to Eespire Them," Transactions of the Asso- 

 ciation of American Physicians, 1895, vol. x. pp. 16-44. 



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