YELLOW FEVER EXPEDITION 
5i5 
introduction as by gnat bite was necessary for reproducing the fever in man, it might 
be that the bacillus could be swallowed by the mosquito from other sources than an 
actual bite on a yellow fever patient. A number of a pupae taken from a cesspool 
(species C. fatigans) were tried, but the results were not satisfactory from the 
external contamination and the extensive cytolysis proceeding in the creature. 
Another attempt made, was to catch mosquitoes coming directly up a large 
ventilating pipe from a sewer, but the whole thing was washed away by a rain shower. 
It seemed possible that a feed of blood might be requisite to supply pabulum for 
the growth or spread of the bacillus within the body of the gnat. 
The implication of a sewage-loving gnat, like C. fatigans^ and the fertile source 
of it in foul water and cesspools was thought possibly to be an explanation of the 
outbreak of cases of yellow fever in apparently isolated and spontaneous manner. 
Altogether about eighty mosquitoes were dissected ; but all of these were not 
examined for the small bacillus ; the method adopted was to remove the salivary sac 
and also the stomach by dissection under a lens ; examine in the fresh state between 
two coverslips in saline solution, and then by drawing the glasses apart they were 
ready for making stained specimens. Out of thirty-five individuals of C. fatigans, 
small bacilli, sometimes in large numbers, occurred sixteen times ; out of thirty 
individuals of S. fasciata it occurred only six times. These were insects caught in 
suspected houses and on a ship with yellow fever. Preparations were made for rearing 
insects from the egg in clean waters, so that when fed upon patients there would be 
no possibility of chance contamination. Although several attempts were made we 
never succeeded in getting the species C. fatigans beyond the young larval stage ; 
with S. fasciata there was no difficulty, the first lot began to hatch out just as 
we were taken ill, and afterwards a new lot was started ; when they were ready I was 
unable to get hold of an early case to feed them upon. So that no observations upon 
reared cleanly mosquitoes which had actually been fed on yellow fever cases were 
made. 
As a working theory of the pathology of yellow fever, derived from these 
observations it was thought that : — 
Supposing the 'small bacilli' found in the 'typical bites,' organs, salivary 
sacs, and stomachs of the mosquitoes and in the intestinal contents were identical in 
nature, and that they were the acting cause of yellow fever, the following working 
theory of the fever could be formulated. At first a subcutaneous introduction of the 
bacilli by the gnats (which might have derived them from patients or by feeding on other, 
e.g. faecal, material) ; affection of the superficial lymphatic glands (in which case the 
infection would seem to take place more frequently in the upper than in the lower 
extremity, as judged by the intensity of the lesions in the glands of the former) ; 
generalization through the system, giving rise to the influenza like first period of 
the fever ; localization of the bacilli in and about the intestinal area, resulting in 
