452 VETERINARY BACTERIOLOGY 



are many unsettled points relative to its morphology. Whether 

 or not it may pass through a cycle of changes that would mark it 

 as certainly protozoan is not definitely known. 



The common anilin dyes used in bacteriological work fail to 

 demonstrate this organism in tissues or in smears. The India- 

 ink method of demonstrating spirochetes may be used as a simple 

 procedure for showing the organisms in smears. This consists in 

 allowing a thin film of India ink to dry upon the smear. The 

 organisms do not take up the ink, and may be recognized as 

 transparent spirals in the black field. They may also be stained 

 by Giemsa's eosin and azur stains. The stain must be freshly 

 prepared. Very satisfactory results are achieved by impregna- 

 tion with silver, particularly for the demonstration of the organ- 

 ism in tissues. t 



Isolation and Culture. The organism has never been cultivated 

 upon artificial media. 



Pathogenesis. Experimental Evidence. The organism may 

 always be found in the primary and secondary lesions of syphilis, 

 and has been repeatedly demonstrated in the tertiary as well, 

 although it is much more difficult to find in the latter stage. It 

 may be found in the internal organs of a syphilitic fetus. An 

 infection has been produced in the cornea and the iris of the rabbit, 

 and the organism shown to be present. The primary and secon- 

 dary lesions of the disease have been produced in the monkey, 

 particularly in the anthropoid apes, and the spirochetes found in 

 each of the stages. The evidence is very strong, therefore, that 

 Spirochaeta pallida is the cause of syphilis. Until the organisms 

 can be injected in pure cultures and produce the disease this evi- 

 dence cannot become indisputable, however. 



Character of Disease and Lesions. In man the primary lesion 

 in the form of a chancre appears in about three weeks after in- 

 fection, usually on or near the external genitalia. It is followed by 

 invasion of the neighboring lymphatics and by progressive en- 

 largement of the lymph-nodes as the disease progresses. Usually 

 about six weeks elapse between the appearance of the primary 

 and secondary lesions. These latter are probably dependent 

 upon an invasion of the blood, and consist of localized skin erup- 

 tions, falling of the hair (alopecia), and the symptoms of generalized 



