162 THE MORE CHRONIC INFECTIOUS DISEASES 



in the laboratory. Noguchi finally succeeded in grow- 

 ing them under anaerobic conditions in a mixture of 

 serum and agar to which a piece of sterile liver or 

 kidney of rabbit had been added. Only rabbits and 

 monkeys among the lower animals can be made to 

 contract syphilis, but of these only the latter shows 

 any similarity to man in the course of the disease. 



FIG. 43. Treponema pallidum appearing as bright refractive 

 body on a dark field, as shown by India ink or ultramicroscope. 

 (Park.) 



When infective crusts from eruptions or serum exuding 

 from them is kept in the test-tube for six hours, 

 infection can no longer be transferred to monkeys. 

 No serum of therapeutic value has as yet been pro- 

 duced, nor can immunity be induced by injecting 

 dead spirochetes. A remedy, salvarsan, consisting of 

 a complex arsenical compound, has been found to 

 cure syphilis. It is efficacious at all stages, stopping 



