Prophylaxis 539 



rats, the soil and the animals forming a circle of habitation for the 

 spirochsetae. It happens rarely that human beings are infected 

 directly through the bites of rats, the infection being usually trans- 

 mitted from the soil where the excreted spirochaetae lodge and thrive. 

 On these grounds we can explain the epidemics of spirochaetosis 

 icterohemorrhagica which occur in coal mines and among farmers in 

 the vicinity. Rats are constant tenants of the mines, and it is 

 known that miners go barefooted (in Japan). A similar statement 

 may be made concerning the transmission of Weil's disease on the 

 battlefields of Europe. There the rats living in the trenches infect 

 the soldiers." 



Spirochetosis icterohemorrhagica is therfore one form of "rat- 

 bite fever," though as will be shown below, not the common form. 

 Inada, Ido, Hoki, Kaneko and Ito, found that when the abdomen 

 of a guinea-pig was cleanly shaven, washed with soap and water, 

 then with alcohol and then dried, 10 out of 13 animals became 

 infected when the spirochaetas were applied to the uninjured skin. 

 They conclude, therefore, that traumatic injury may be unnecessary 

 to bring about infection, the micro-organisms finding their way into 

 the body through the skins of persons exposed to wet soil con- 

 taining them. 



Prophylaxis. — ^The necessity of exterminating rats through whose 

 urine the chief dissemination of the spirochaetae takes place is an indis- 

 pensable factor in preventing the infection. In mines and military 

 trenches, drainage and drying of the soil are eminently desirable 

 as a secondary procedure, tending to destroy the micro-organisms. 

 Where this is not possible and the localities must be occupied, 

 advantage might be taken of the observations of Inada, Ido, Hoki, 

 Ito and Wani that the spirochaetae die in soil that is acid, to apply 

 a chemical effecting the necessary change of reaction to the earth 

 of the trench or mine concerned. 



Ido, Hoki, Ito, and Wani* have attempted to produce active im- 

 munity in guinea-pigs and in men by vaccination with a preparation 

 made as follows : To a liver emulsion or a pure culture, which con- 

 tained 10 to 15 spirochaetae in a single field (Jf 2 oil immersion, ocular 

 III under dark field illumination) carbolic acid was added in the pro- 

 portion of 0.5 per cent., after which the mixture was left in the ice- 

 box for a week. The clear supernatant fluid was employed for the 

 injections and administered to guinea-pigs intraperitoneally in doses 

 of 2-4 cc, three times at 7-9 day intervals. An uncertain degree 

 of immunity was developed. 



They also undertook the immunization of a horse through in- 

 oculation with the vaccine and after having demonstrated the appear- 

 ance of immune bodies in the blood of the horse, proceeded to the 

 active immunization of man. They found that by the employment of 

 a vaccine ten times as strong as that originally employed for guinea- 

 * Jour. Exp. Med., igi6, xxiv, p. 471. 



