1903-4. | ULTRAMICROSCOPIC ORGANISMS. tS 
many have been the bacteria which have been isolated and made responsible 
for its ravages. 
One of the earliest investigators was Stenberg, and his work is a really 
wonderful monument to the value of negative evidence. For although 
he isolated an immense variety of bacteria from yellow fever patients, he 
did not venture to connect any one of them specifically with the disease, 
and only risked calling attention to the more frequent occurrence of a cer- 
tain form which he called bacillus x. It is not necessary to enumerate 
all the subsequent students of this subject, but some years ago Sanarelli, 
an Italian, trained at the Paris Pasteur Institute, went out to South America 
to study yellow fever, and came back with the announcement that he had 
at last discovered the cause in a form which he called bacillus icterogenes. 
He was a tried and careful observer, and his work had the seal of 
the Pasteur Institute, and it was accepted by the majority of bacterio- 
logists, so much so that we kept our cultures of bacillus icterogenes under 
lock and key for fear we should be responsible for the spread of the dreaded 
Yellow Jack. 
However, doubts began to arise when Stenberg demonstrated that 
Sanarelli’s bacillus was his bacillus x, and a little later Major Reed demon- 
strated that both the Sanarelli bacillus and bacillus x were simply varieties 
of the hog cholera bacillus. 
With the discrediting of bacillus wcterogenes the work had to begin 
all over again, and with the finish of the Spanish-American War Reed 
and his associates proceeded to Havana to study yellow fever in one of its 
endemic centres. 
But they went with the accumulated results before them of a series 
of very important investigations into etiology and disease transmission, 
viz., with the results of Manson’s and Ross’s work in regard to the trans- 
mission of malaria by the mosquito. As early as 1881, however, a Havana 
physician, Dr. Carlos Finlay, had propounded the view that the mosquito 
was responsible for the transmission of yellow fever and it was natural 
that Reed and Carroll should turn their attention to the influence of the 
mosquito. 
The results of the work of these investigators was to show that yellow 
fever could be communicated by blood taken from patients on the first 
or second day of the disease ; that it could be transmitted by a mosquito 
(Stegomyia fascvata) which had sucked the blood of a yellow fever patient, 
but only 12 or 25 days after the insect had had its meal of blood, that is, 
the parasite required to live a certain time in the mosquito. Further 
they showed conclusively that it could not be transmitted by fomites. 
The practical outcome of this work has been that by excluding mos- 
