Transmission 529 



organ is not essentially changed histologically, but seems to be merely 

 hyperplastic. The liver is enlarged, but here, again, specific changes 

 may be absent. In some cases a pallor of the centers of the lobules 

 may depend upon numbers " of parasite-containing cells, partly 

 degenerated. 



The yellow bone-marrow becomes absorbed and red tissue takes 

 its place, as in most profound anemias. 



Transmission. — Rogers' observation, that the round bodies grew 

 into flagellate bodies at temperatures much below that of the human 

 body, led Manson to conjecture that the extrahuman phase of the 

 life of the organism took place at similar low temperatures in the 

 soil or in water. Patton* found that a number of cases sometimes 

 occurred in the same house, while neighboring houses were free, and 

 thought this suggested that a domestic insect might be the distribut- 

 ing host. Later, Pattonf reported a very thorough study of insects 

 in relation to kala-azar, in which after a long series of experimental 

 investigation, he came to the conclusion that the Indian bed-bug, 

 Cimex rotundatus, is the specific invertebrate host of Indian kala- 

 azar. It seems that in order that the parasites shall mature in the 

 bed-bug, and undergo those changes that shall result in the insect's 

 infectivity, the bug must receive one full meal of the infected blood. 

 If a second meal is taken, the digestive condition in the bug's aHmen- 

 tary canal is changed, and instead of continuing to develop, the 

 parasites die out. When the conditions are all favorable, Patton 

 found that the flagella,tes continued to multiply actively from the 

 fifth to the eighth day. By the twelfth day practically all had 

 reached the postflagellate stage and were only found in the stomach 

 of the bed-bug. These results convince Patton that Cimex rotund- 

 atus is the definitive host, but the proof is lacking. No animal 

 is known to be sufficiently susceptible to Leishmania donovani, to 

 acquire anything resembling Kala-azar, therefore there is none 

 that the bug can successfully infect. Human experiment with 

 so fatal a disease being out of the question, the case rests at this 

 point. RowJ has, however, shown that when a monkey, Macacus 

 sinicus, is inoculated cutaneously or subcutaneously with a three- 

 weeks-old culture of Leishmania donovani, a cutaneous or sub- 

 cutaneous lesion may result. This may facilitate future studies 

 with biting insects. 



It maybe, however, that Patton and others are wrong in thinking 

 that the flagellate stage at which the parasites arrive in the bed-bug 

 is the infective stage, and have, therefore, gone astray. Bayon§ 

 points out that Leishmania infantum is infective for dogs and 

 monkeys in the rounded or oval stages, not in the elongate or 

 cultural stages, and that the same may be true of Leishmania dono- 



* "Scientific Memoirs of the Government in India," 1907, No. 27. 

 t "Brit. Med. Jour.," 191 2 11, 1194. 

 I "Brit. Med. Jour.," 1912, n, 1196. 

 § "Brit. Med. Jour.," 1912, n, 1197. 



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