208 SPIRILLA. 



nema pallida. He called it the Spirochaeta refringens (Plate VI, 

 Fig. 2). Its curves are fewer and more rounded, and in stained 

 preparations it stains more deeply than Treponema pallida. 

 Schaudinn regards its finding as accidental and unimportant. 

 For staining in tissues Levaditi's method is most used, as follows : 



1. Cut fresh tissue in cubes 2-4 m.m. square. 



2. Harden in solution formalin (10 per cent.) for twenty- 

 four hours. 



3. Wash in distilled water. 



4. 96 per cent, ethyl alcohol for twenty-four hours to de- 

 hydrate. 



5. Wash in distilled water. 



6. Place in 3 per cent, nitrate of silver solution for three to 

 five days at a temperature of 37.5 C. and in the dark. 



7. Give the tissue a short rinsing in distilled water. 



8. Place for twenty-four hours in fresh solution of pyrogal- 

 lic acid, 2 per cent., formalin, 5 per cent., in distilled water. 



9. Wash in distilled water. 



10. Dehydrate in ethyl alcohol of graded strength, from 25 

 per cent, to absolute. 



11. Imbed in paraffin and make thin sections. 



12. Mount and examine. 



By this method the treponema show as blackened, untrans- 

 parent spirals. 



Pathogenesis. The treponemata are pathogenic for all races 

 and ages of man. They have been found in all stages of syph- 

 ilis in the chancre, lymph-nodes, and even in gummata. In 

 cases of congenital syphilis treponemata have been demon- 

 strated in all the foetal organs. 



Animal Inoculation. After many failures by injection of 

 syphilitic material, successful inoculations have been made by 

 many investigators by the implantation of pieces of fresh 

 syphilitic material under the skin of the eyelid in the genital 

 mucous membrane. In these cases successful inoculations 

 were followed by definite syphilitic lesions, and Treponema 

 pallida recovered from the primary sore and the enlarged 

 lymphatics. 



Immunity. The fact that one attack o syphilis confers 



