622 Insects and Disease 



parasites which by hypothesis the gametocytes were expected to develop 

 into. This required not only familiarity with the histology of gnats, but a 

 laborious search for a minute organism throughout the whole tissues of each 

 individual insect examined a work of at least two or three hours for each 

 gnat. But the actual labor involved was the smallest part of the difficulty. 

 Both the form and appearance of the object which I was in search of, and 

 the species of the gnat in which I might expect to find it, were absolutely 

 unknown quantities. We could make no attempt to predict the appearance 

 which the parasite would assume in the gnat; while owing to the general 

 distribution of malarial fever in India, the species of insect concerned in the 

 propagation of the disease could scarcely be determined by a comparison 

 of the prevalence of different kinds of gnat at different spots with the preva- 

 lence of fever at those spots. 'In short, I was forced to rely simply on the 

 careful examinations of hundreds of gnats, first of one species and then of 

 another, all fed on patients suffering from malarial fever in the hope of 

 one day finding the clue I was in search of. Needless to say, nothing but 

 the most convincing theory, such as Manson's theory was, would have sup- 

 ported or justified so difficult an enterprise. 



" As a matter of fact, for nearly two and a half years my researches were 

 almost entirely negative. I could not obtain the correct scientific names of 

 the various species of gnats employed by me in these researches, and con- 

 sequently used names of my own. Gnats of the genus Culex (which abound 

 almost everywhere in India) I called 'gray' and 'brindled' mosquitoes; 

 and it was these insects which I studied during the period referred to. At 

 last, the particular nugatory results which had been obtained with gnats 

 of this genus determined me to try other methods. I went to a very mala- 

 rious locality, called the Sigur Ghat, near Ootacamund, and examined the 

 mosquitoes there in the hope of finding within them parasites like those of 

 malaria in man. The results were practically worthless (except that I 

 observed a new kind of mosquito with spotted wings); and I saw that I 

 must return to the exact methods laid down by Manson. The experiments 

 with the two commonest kinds of Culex were once more repeated only to 

 prove once more negative. The insects, fed mostly on cases containing 

 the crescentic gametocytes of Hcemomenas prcecox, were examined cell by 

 cell not even their excrement being neglected. Although they were known 

 to have swallowed Haemamcebidae, no living parasites like these could be 

 detected in their tissues the ingested Haemamcebidae had in fact perished in 

 the stomach-cavity of the insects. I began to ask whether after all there 

 was not some flaw in Manson's induction; but no I still felt his conclusion 

 to be an inevitable one. And it was at this moment that good fortune gave 

 me what I was in search of. 



" In a collecting-bottle full of larvae brought in by a native from unknown 



