170 TROPICAL MEDICINE AND HYGIENE 



the parasites increased in size, became granular, and the 

 body became elongated, the macronucleus enlarged and 

 the micronucleus migrated to the thicker end of the 

 organism from which a flagellum arose. The protrusion 

 of the flagellum was preceded by the formation in the 

 cytoplasm surrounding the micronucleus of a rounded 

 mass which stained with eosin, the rest of the cytoplasm 

 staining blue with Leishman's stain. 



In one instance long, flagellate forms were developed 

 within twenty-four hours, these chiefly occurring in 

 pairs. In later experiments (1905) Rogers has found 

 that the development of flagellated forms from kala-azar 

 parasites takes place more freely and with greater regu- 

 larity in an acid than an alkaline medium, and that 

 sterility of the medium is essential. This has led him 

 to suggest that the intermediate host of the parasite 

 might be the bed-bug, the intestinal contents of which 

 he found supplied these conditions. Working on this 

 hypothesis, Patton has announced that he has been able 

 to trace the complete cycle of the parasites up to com- 

 pletely developed flagellates in certain tropical bed-bugs, 

 and that in his opinion there is no doubt that the Indian 

 bed-bug, Cimex rotundatus, transmits the disease. 



The rarity of the occurrence of the parasites in the 

 peripheral blood has been advanced as an argument 

 against this method of infection. Donovan has, how- 

 ever, shown that they occur in the peripheral blood in 

 the leucocytes intermittently in all cases of kala-azar, and 

 at times may be fairly numerous. It must also be re- 

 membered that trypanosomiasis can often be transmitted 

 by the injection of blood, the microscopical examination 

 of which fails to reveal any parasites. 



In the Assam epidemics kala-azar spread slowly from 

 village to village along the lines of communication. 

 Isolated villages, or those to which persons from outside 

 w r ere not admitted, remained free from attack, and the 

 common history of infected villages was that some person 

 had arrived there suffering from the disease ; after a short 



