that the number of flagellates found in the gut of a bug after a 

 few days, varies directly with the number of parasites ingested, 

 fn (Oriental sore tlie number of Leishwaiiia taken up must be 

 very small and there is never a large infection with flagellates; 

 while in Patton's last experiments, in which the bugs were fed on 

 a heavily infected case of Kala Azar with numerous parasites in 

 the peripheral bUxxi, he obtained large numl)ers of flagellates. 



If the bug were the true host of the Leishmania, complete 

 infection of the gut would take place whether many or few para- 

 sites had been ingested, a longer time only being required to 

 show^ a large infection when the parasites were few. In insects 

 infecting themselves with Herpetoinonas the author thinks it is 

 not necessary that large numbers should be ingested to secure 

 heavy infection. 



Effect of a second feed of blood on the flagellates in Insects. 



Patton has shown that a second feed of blood is fatal to the 

 flagellate forms of Leishmania in the bug. This the author 

 regards as fatal to the bug hypothesis. He kept fleas under 

 observation, some infected with Herpetomonas and others with 

 Trypanosoma lewisi. One flea had 16 feeds of human blood in 

 two months. The faeces voided during feeding were constantly 

 infected with Herpetomonas in large numbers, so that active 

 multiplication must have gone on. Two other fleas in the same 

 way showed the small infective trypanosomes, characteristic of 

 T. lewisi, in the faeces on all occasions. The author argues that 

 the flagellates were not destroyed because they were living on 

 their true host. Patton has shown that the natural Herpetomonas 

 of Culex fatigans disappears from the insect when it has a feed 

 of blood, probably because, being really a flagellate of the larva 

 of the mosquito, it finds itself in an unnatural environment. 



Miss Robertson has found that batches of Glossina fed on 

 cases of human trypanosomiasis show a greater percentage of 

 individuals infected if they have had only a single feed of blood. 

 The explanation in this case is not clear, as it is known that an 

 infected Glossina may infect a series of animals at intervals of 

 several days. Patton regards this effect of a second feed of 

 blood as explaining the tendency of kala azar to remain localised 

 in Madras and Oriental sore in Cambay. But this assumption 

 contains a fallacy. It is not as a rule the intermediate host 

 which transports the infection from place to place, but the 

 reservoir (frequently man himself) that travels about to places in 

 which the intermediate host is to be found. Trypanosomiasis, 

 yellow fever and malaria are carried about by the moving reservoir 

 — Man — not by Glossina, Stegomyia and Anopheles ; and plague 

 is carried by rats. This appears to be a far more reasonable view 

 of the means of dispersal of kala azar and Oriental sore. The 

 intermediate host may of course be transported, but this is a 

 mode of spread quite subsidiary to that caused by the movements 

 of man himself. 



28112 A 2 



