113 

 3 



rate itself from the body and to shoot 

 vigorously away. So vigorously, and with 

 such apparent intention does it do so, that 

 it often sets the surrounding corpuscles 

 bobbing like a row of corks in a tideway. 

 For years a discussion raged over this 

 phenomenon. Why did the organism 

 throw out these arms only after leaving 

 the body ? The octopus- like creature, or 

 male gamete, was never seen in blood 

 immediately after its removal, but de- 

 veloped from certain of the parasites, but 

 not all, in a short time when kept warm 

 and moist. If not kept warm and moist 

 it did not develop. Moreover, why was it 

 that only some of the amoeloid organisms 

 threw out arms and not all ? And why 

 did one or more of the arms when thrown 

 out cast loose from the rest and dart 

 away? 



Upon these and similar facts Dr. 

 Manson, then of Hong Kong, formulated 

 in 1894 that fine piece of inductive 

 reasoning which will always be associated 

 with his name. Earlier observers had 

 from time to time made suggestions of a 

 similar nature, but it was reserved for 

 Manson to formulate from the known 

 facts a true scientific hypothesis. Being 

 a parasite, he argued, the malarial 

 organism must, like most other parasites, 

 live for part of its existence outside the 

 human body in another host. The 

 octopus-like male gamete does not come 

 into existence until after leaving the 

 body, and while in the body the parasite 

 is incapable of liberating itself by its own 

 efforts. No traces of the parasite could 

 be found in any of the discharges 

 of the patient. It was there- 

 fore probable that it was re- 

 moved from the body by some blood 

 eating creature. Manson had previously 

 performed some brilUant researches into 

 the conveyance of certain other blood 

 parasites by mosquitoes, and he was led 

 to the conclusion that some distmct kind 

 of mosquito was the probable agent, and 

 that the male gamete formed the first stage 

 of the extra corporeal development of the 

 parasite in its new host. I need scarcely 

 remind you that in all its main pomts 

 Manson's hypothesis has been proved 

 correct. 



Then Captain (now Major) Ross, of 

 the Indian Medical Service, took up the 

 work of investigating the development in 

 the mosquito. It must be remembered 



that he^ began with practically no know* 

 ledge of the classification, structure, or 

 habits of mosquitoes, since at that date 

 (1895) comparatively little was known 

 even to dipterologists, and that most of 

 his work was done in an up-country 

 Indian station far from the equipment 

 and facilities of a modern laboratory. For 

 two and a-half years he worked on, dis- 

 secting and examining, cell by cell, 

 hundreds of mosquitoes without result, 

 and attempting feeding experiments in 

 vain. It is natural that after such an ex- 

 tended series of negative results he was 

 beginning to suspect a flaw in ManFon's 

 theory. Then came light. A peculiar 

 species of mosquito, which he had once 

 before noticed in a very malarious locality 

 as possessing dappled wings and laying 

 boat-shaped eggs, was fed upon the blood 

 of a malarial patient, and on dissecting it 

 he found, for the first time, in its tissues 

 granules of that coal black substance 

 which I mentioned as being called mela- 

 nin, and as chara'^teristic of malarial 

 fever, and in its stomach walls certain 

 oval cells. These discoveries practically 

 solved the problem. The dappled winged 

 mosquito with boat shaped eggs belonged 

 to the genus Anopheles, and the oval cells 

 in the stomach wall were the developing 

 parasites of remittent malarial fever. 



The rest was comparatively easy once 

 these facts were known. 



The plague scare amongst the natives 

 made it necessary for Ross to pursue his 

 researches into the development of the 

 organism in the mosquito by means of a 

 closely similar organism conveyed by a 

 Culex to birds, since blood feeding experi- 

 ments from human beings became practi- 

 cally impossible, but he had solved the two 

 great problems in the way of the triumph- 

 ant proof of Manson's hypothesis, and 

 that hypothesis was proved to be soundly 

 founded. He had, moreover, distinguished 

 the true malefactor — the Anopheles 

 mosquito— from the innocent Culex, and 

 his previous difficulties were to some ex- 

 tent explained by the silent retiring and 

 unobtrusive habits of the former genus. 

 The differences between Culex and 

 Anopheles are clear enough nowaday?, 

 but it is proverbially easy to be wise after 

 the event. We must always rememter 

 Ross in his up-country bungalow working 

 on without recognising this shy and un- 

 obtrusive genu8]from the myriads of Culic ea 



