V. OWN OBSERVATIONS ON YELLOW FEVER ETIOLOGY 
On the accompanying table will be found the results of our examinations of the 
post-mortem material. 
The course of our investigation was chiefly directed at first to the search for 
some protozoal parasite, but it so happened that, especially in the specimens of the 
mesenteric glands out of the first autopsy, we were much struck with the presence of a fine 
minute bacillus in some quantity. At the next autopsy, especially in the observation of 
the fresh spleen juice, we were so much struck with certain curious elongated 
structures of protoplasmic nature, that we spent much time in searching for these 
and other similar bodies in tissues of subsequent autopsies and in blood of living 
patients. Eventually we proved that these structures were artificial, by producing 
them from our own blood. About the same time we came to the conclusion that 
possibly the investigation of mosquitoes captured in suspected houses might give 
a lead for further work. Almost the first of these (a C. fatigans) dissected on 6th 
December, 1900, showed large numbers of what instantly reminded me of the 
bacillus we had encountered at the first autopsy, some others gave a like result. We 
then commenced to stain and examine the material prepared from the other autopsies 
for this organism particularly. Owing to the scanty numbers which were found in 
given specimens, this process of examining took some time, and the thorough search 
through the old material was not finished when we were taken ill ; meanwhile, material 
obtained at other autopsies was examined, and careful search again and again revealed 
its presence. Since there was a suspicion that possibly a bacillus found in such small 
numbers might be merely an accidental incomer, attention was paid to see where it 
could come in. The points at which contamination might occur were in the prepara- 
tion of the film from the organ, this was excluded by care in searing and using 
recently-heated capillary tubes to obtain the juice ; the freshness of the cadaver at 
the post-mortem and the frequent sterility of the organs by culture showed that no 
gross contamination usually took place. 
The possibility of the presence of organisms on the coverglasses from the water 
in which they had been washed led us only to employ ones which had been 
thoroughly heated by the spirit lamp on a piece of wire gauze nearly to redness just 
before use. Since the organisms clearly appeared in the film and not superposed to it 
we did not think it likely that it could have got in during the staining of the dried flamed 
film ; however, besides using the stain as heretofore with five per cent, carbolic acid in 
its constitution, we tried washing out also in carbolic, and only using recently sterilized 
Petri dishes for the stain and the washing. It was difficult to see what other 
