RELATIONS OF SPIRILLUM TO DISEASE. 447 



found that after the spirilla had disappeared from the blood, 

 the disease could be produced in another animal by inocu- 

 lations with spleen pulp, in which the spirilla were contained 

 within the leucocytes, thus showing that they were living 

 and active in the spleen. It is to be noted in this con- 

 nection that swelling of the spleen is a very marked feature 

 in relapsing fever. These observations have been entirely 

 confirmed by Soudakewitch, who also showed that the 

 destruction of the spirilla in the spleen was an extremely 

 rapid one, as they were all destroyed ten hours after their 

 disappearance from the blood. He also produced the 

 disease in two monkeys from which the spleen had been 

 previously removed, the animals having been allowed to 

 recover completely from the operation. In these cases the 

 spirilla did not disappear from the blood at the usual time, 

 but rather increased in number, and a fatal result followed 

 on the eighth and ninth days respectively. Post mortem he 

 found the spirilla in enormous numbers throughout the 

 blood vessels, and in the portal vein they almost equalled 

 the red blood corpuscles in number. By these experiments 

 it would appear to be established that the spleen has an 

 important function in the destruction of the organisms. It 

 has not been shown, however, why the organisms disappear 

 from the blood at a particular time and accumulate in the 

 spleen. 



In the case of the human subject it has been found that 

 a second attack of the disease can follow the first after a 

 comparatively short period of time, and it is often said that 

 one attack does not confer immunity. It is probably rather 

 the case that the immunity conferred is of very short duration. 

 The course of events in the disease might be explained by 

 supposing that immunity of short duration is produced during 

 the first period of pyrexia, but that it does not last until 

 all the spirilla have been destroyed, some still surviving in 

 internal organs. With the disappearance of the immunity 

 the organisms reappear in the blood, the relapse being, 

 however, of shorter duration and less severe than the first 

 attack. This is repeated till the immunity lasts long enough 



