SPIROCHETES 259 



reaction and by pigeon inoculations. A minute amount of a culture 

 of S. Metchnikovii injected subcutaneously into a pigeon gives 

 rise to a rapidly fatal septicemia ; the same quantity of a cholera 

 culture produced practically no effect. 



S. Massaval and S. Finkler-Prior, both isolated from feces, and 

 S. Deneke isolated from cheese, all closely resemble the cholera 

 bacillus, but they do not give a specific reaction with cholera- 

 immune serum. 



SPIROCHETES 



Because the structure of certain spiral organisms appears to 

 be more complicated than that of many bacterial forms, and be- 

 cause several observers have found structural similarities between 

 them and the protozoa, they have come to be regarded by many 

 bacteriologists as members of the latter group, or as a separate 

 genus intermediate between bacteria and protozoa. Their classi- 

 fication, however, is still undecided. The discovery that a spiro- 

 . chete was the cause of syphilis brought the organisms into great 

 prominence, and since then many varieties have been isolated and 

 studied. The diseases produced by them fall into two main groups : 

 one usually transmitted by contact and in which infection is pri- 

 marily of the tissues, as in syphilis and yaws; and the second, 

 a blood infection accompanied by fever and transmitted by an 

 animal parasite. 



Treponema Pallidum (Spirocheta pallida) . 



Schaudinn and Hoffman, working together in 1905, found in the 

 fresh exudates of syphilitic lesions a spirochete which they thought 

 might be the cause of the disease and to which they gave the name 

 Spirocheta pallida. Later they decided that the organism was 

 sufficiently distinctive to be placed in a separate genus and they 

 changed the name to Treponema pallidum. 



Morphology and Staining. The organism appears as a long, 

 slender spiral averaging about 10 p in length and 0.3 //. in diam- 

 eter and with three to twenty small, sharp, regular curves. The 

 ends are pointed and at each is a fine flagellum (Fig. 37) . Movement 

 may be of gliding to-and-fro nature, rotation on the long axis, or 



