IMMUNITY 511 



were ingested in large numbers by the microphages or poly- 

 morphonuclear leucocytes. Within these they rapidly under- 

 went degeneration and disappeared. It is to be noted in this 

 connection that swelling of the spleen is a very marked feature 

 in relapsing fever. These observations were confirmed by 

 Soudakewitch, who also found that when the disease was pro- 

 duced in splenectomised monkeys (cercocebus fuliginosus) the 

 spirochsetes 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. Recent observations, 

 however, indicate that, as in the case of so many other diseases, 

 the all-important factor in the destruction of the organisms is 

 the development of antagonistic substances in the blood. Lamb 

 found in the case of the monkey (macacus radiatus) that the 

 removal of the spleen of an animal rendered immune by an 

 attack of the disease did not render it susceptible to fresh 

 inoculation, and attributed the immunity to the presence of 

 bactericidal bodies in the serum. He found, for example, that 

 in vitro the serum of an immune animal brought the movements 

 of the spirochsetes to an end, clumped them, and caused their 

 disintegration ; and further, that when the spirochaetes and the 

 immune serum were injected in one case into a fresh monkey no 

 disease developed. In opposition to Soudakewitch, Lamb found 

 that with a monkey from which the spleen had been removed, 

 death did not occur after it was inoculated with the spirochsetes. 

 Observations by Sawtschenko and Milkich, Novy and Knapp, 

 and Rabinowitsch, also show that in the course of infection there 

 are developed anti-substances of the nature of immune-bodies, with 

 protective properties, and agglutinins. Novy and Knapp pro- 

 duced a " hyper-immunity " in rats by repeated injections of blood 

 containing the spirochsetes, and found that the serum of such 

 animals had a markedly curative effect, and could cut short the 

 disease in rats, mice, and monkeys. The course of events in the 

 human 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 organisms have been 

 destroyed, some still surviving in internal organs or in tissues 

 where they escape the action of the serum or phagocytosis. 

 With the disappearance of the immunity, the organisms appear 

 in the blood, the relapse being, however, of shorter duration and 

 less severe than the first attack. This is repeated till the im- 

 munity lasts long enough to allow all the organisms to be killed. 

 It is possible, however, that the survival of resistant spirochsetes, 

 or " mutants," may play a part in the production of the relapses. 



