GENERAL CHARACTERS OF SPIROCH^TES. 31 



consequently held that morphology does not constitute 

 a valid test of species. 



These observations are sufficient to indicate that con- 

 siderable doubt must be felt as to the constancy of form 

 among the small spirochaetes ; and when it is remembered 

 that the identification of such a form as Sp. pallida de- 

 pends entirely upon its morphology, and that many 

 forms have been described in conditions other than 

 syphilis which can only be differentiated by experts from 

 this spirochaete, the uncertainty that must continue to 

 prevail as to relations of the small spirochastes to each 

 other and to the morbid conditions with which they 

 are associated, is undeniable. 



HABITAT. 



The only free-living spirochaetes at present known 

 are Sp. plicatilis and Sp. daxensis which are found in 

 fresh water. Sp. polyspira is a saprophyte found in 

 decaying vegetable matter (potato). The rest of the 

 large spirochastes are saprophytes or commensals in the 

 alimentary canal of various shell-fish. Of the smaller 

 forms many are apparently saprophytes on the surface 

 of ulcerative lesions ; others are also saprophytic within 

 the intestines of various animals. A few only are 

 definitely pathogenic, being capable of multiplying 

 within the living tissues of an animal host and there 

 producing poisonous products. 



CULTIVATION. 



Spirochaetes have never been satisfactorily culti- 

 vated; that is to say, they have never been isolated 

 in artificial media and passed from culture to culture. 

 Many authors have stated that they have succeeded in 

 producing multiplication of spirochaetes on laboratory 

 media. Thus Duval and Todd kept Sp. duttoni alive 



