LEISHMANIA DONOVANI 673 



The question arises, given that the Leishmania donovani is 

 the cause of kala-azar, how is infection spread'! On this we 

 have as yet no certain information. Water has been looked on 

 as the carrier of infection, but the possible relationship of the 

 organism to the trypanosomata naturally suggests the idea of an 

 insect as an intermediary, and Rogers adduced some evidence that 

 the bed-bug is the extra- human host. Patton fed the common 

 insect parasites of man in Madras on patients whose peripheral 

 blood contained the Leishmania, and observed the flagellate stage 

 in the bug, cimex rotundatus, especially after a single feed with 

 human blood, which, however, as stated above, contains sub- 

 stances inimical to the full development of the parasite. As in 

 all experiments of the kind, difficulties arise in consequence of 

 the great variety of flagellates which normally inhabit the 

 intestine of insects. The fact that the Leishmania may occur 

 only in small numbers in the peripheral blood was advanced as 

 an argument against infection taking place by means of a blood- 

 sucking insect, but often considerable numbers occur in the 

 blood, and, apart from this, invisible spirillary forms may be 

 instruments of infection. It must be stated that up to the 

 present the means by which infection takes place in kala-azar 

 has not been determined. 



Though results obtained in different parts of the world vary 

 somewhat, animals such as the monkey, the dog, and the mouse 

 have, in a proportion of cases, been infected with the parasite as 

 it occurs in human lesions and also in cultures. The intra- 

 peritoneal route is the best, and both when the animals have 

 died and have been killed Leishmanias have been found in such 

 situations as the spleen, the liver, the bone marrow. Feeding 

 experiments have usually been unsuccessful, but one or two 

 positive results are recorded. In India the examination of dogs 

 which have been in contact with kala-azar cases has not yielded 

 evidence that natural infection occurs in these animals. 



With regard to kala-azar as a whole, we may say that we are 

 dealing with a distinct disease fairly widespread in various sub- 

 tropical regions. All attempts to include it among the malarial 

 cachexias, which clinically it so much resembles, have failed. 

 In this atypical cachexial fever there is always present a parasite 

 of very special characters belonging or closely allied to a group 

 which contains many varieties capable of giving rise to similar 

 diseases. Beyond this we cannot go, but there is strong pre- 

 sumptive evidence of the parasite described being the cause of 

 the disease. 



Methods of Examination. — The Leishmania donovani can be 



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