52 SPIROCILETES. 



action. So much irritation could hardly be attributed 

 to the presence of only a few degenerate spirochaetes. 



4. The fact that the Sp. pallida is found in the lesions 

 artificially produced by inoculation of lower animals 

 with syphilitic material constitutes a two-edged argu- 

 ment, since the only animals which are definitely sus- 

 ceptible to syphilitic infection are the apes, while the 

 spirochaete has been found living in dogs, cats, rabbits 

 and guinea-pigs. It is necessary to assume that the 

 pathogenic agent of syphilis can exist as a saprophyte in 

 lower animals which are insusceptible to the disease 

 a condition which is at least unusual in the case of 

 infective organisms. Otherwise it must be held to be 

 saprophytic in both cases. In this connection the 

 observations of Gaylord on the transmission of spiro- 

 chastes in mice may be brought into comparison. This 

 observer found spirochaetes in certain cases of cancer 

 in mice, and on inoculating other mice with emulsions 

 of the tumours, he found that the spirochaetes were 

 also discoverable in the growths which resulted. The 

 natural inference that the spirochaetes were the cause 

 of the cancer was, however, proved to be erroneous; 

 and it appeared that the organisms were frequently 

 present in mice and could be transmitted from one to 

 another, but were harmless parasites of these animals. 

 Of course, the parallel is not very close, since the Sp. 

 pallida is not found in normal men or animals, but the 

 possible transmission of spirochaetes which are in no 

 sense pathogenic must be noted. 



5. The discovery of spirochaetes, very like Sp. pallida 

 in the closely allied diseases, yaws and ulcerative gran- 

 uloma of the pudenda, would seem to constitute an ad- 

 ditional argument in favour of the Sp. pallida being 

 the true cause of syphilis. Herein also lies, however, a 

 certain source of difficulty. It is generally said that the 



