132 DISCUSSION
directly into the skin of a fresh host they would pro- bably multiply more readily and give rise to much local reaction, but they would not tend to invade the organism of the host ; their tendency must be to travel to the exterior for the purpose of being taken up by an appropriate host, in the body of which they might accom- plish their sporogony. Thus it might well be that the general infection could only arise from the inoculation of young forms (sporozoits) by such insects as might subserve them as definitive hosts, whilst the localized cutaneous form might be the result of the direct inocula- tion of adult forms (sporonts) conveyed in a mechanical way either by insects or contaminated objects. Certainly asexual multiplication could not continue indefinitely, especially in the same host, and they knew perfectly well that in all animals presenting asexual multiplication a sexual act, or some other form of rejuvenation, was necessary from time to time for the continuance of the species. He believed, therefore, that it was not unreason- able to surmise with Manson that kala-azar might be a general infection caused by the " Leishman parasite " and conveyed from man to man, or from certain animals to man, by the agency of the rounded bed-bug or of some other insect capable of subserving its sporogony, and Oriental sore a localized cutaneous manifestation, due to the same parasite, conveyed from man to man, or from certain animals to man, through the agency of the common house-fly or some other insect which might or might not be necessarily concerned in its development.
The question was one of the highest importance with regard to the prophylaxis of this deadly and widespread scourge of tropical and subtropical countries, and con- sidering how easily it could be done, it was surprising that no one had attempted hitherto to prove or disprove the hypothesis.
