456 YELLOW FEVER. 



doubt that the bacillus icteroides is the cause of yellow 

 fever. It must be looked on as settling chiefly in the liver 

 and kidneys and there producing very powerful toxines 

 whose chief effects are on the cells of these organs and 

 on the small blood vessels of the body, thus causing the 

 rupture of vessel walls, which frequently results. These 

 grave actions of the toxines open up a path for infection 

 by the other organisms we have noted as frequently 

 occurring in conjunction with the B. icteroides in the 

 bodies of those dead of the disease. To such secondary 

 infection is due the variability in the clinical types met 

 with, though probably another cause is interference with 

 the functions of the kidneys when the affection of these 

 organs predominates. There is evidence that when the 

 secondary infections commence their results are inimical 

 to the vitality of the B. icteroides, a fact which would to 

 some extent explain the many failures to find the latter in 

 cases of yellow fever. 



These results have not thrown any light on the channels 

 of natural infection. Sanarelli has shown that between 

 moulds and the B. icteroides there exists a symbiosis favour- 

 able to the latter. This is a possible explanation of the 

 well-known belief that the infection has a special tendency 

 to hang about the holds of ships. The non-occurrence of the 

 B. icteroides in the intestinal canal is interesting, as several 

 observers had tried unsuccessfully to inoculate themselves 

 by means of the black vomit. 



Immunity against the B. Icteroides. The serum 

 of yellow fever patients is said by Sanarelli to clump 

 the B. icteroides. Other observers have confirmed the 

 observation, the most appropriate dilution being i : 40. 

 The reaction is said to appear on the second day. 

 The smaller animals are unsuitable for immunisation on 

 account of their great susceptibility to toxic action ; but 

 horses have been immunised by careful injections of filtered 

 cultures, cultures killed by ether and living cultures suc- 

 cessively. The process is, however, a very tedious one. 

 The serum of such a horse was found capable of saving 



