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 Haemamcebidse, 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 
