502 
THOMPSON YATES LABORATORIES REPORT 
Whilst in the main the incubatory phase was so constant that the illness began 
during the course of the fourth day, there are two examples of considerable excess, 
viz., Nos. i and 4 ; in both of which the number of presumably infecting gnats was 
three and four respectively ; thereby contrasting with cases 1 and 5, in which but a 
single gnat conferred the infection. Without laying too much stress upon variations 
of this character especially, because the experiments are naturally few in number, it is 
perhaps not unfair to remark that their validity depends upon the constancy of the 
watch kept upon the individuals after inoculation, and in the case of No. 16 daring 
the latter part of the quarantine period. 
Another point of interest is the comparative mildness of the illness produced 
and the absence of fatal result.* It may be noted that the naturally acquired and fatal 
attack, which unfortunately carried off poor Lazear, was ascribed to the bite of a 
single mosquito. In personal conversation with Major Reed I gather that he attributes 
these results to the early stage at which the illness was recognized and treated by 
rest. Another point in regard to the naturally acquired fever is that in many, if not 
in most cases, exposure to infection leads up to, if not after, the time the patient is 
taken ill. 
Major Reed and his colleagues further showed that the blood of yellow fever 
patients, at any rate at the early stage, is capable of conferring the illness by the 
direct transference of blood from sick to healthy ; thus 2 c.c. taken early on the second 
day, 1 77 c.c. taken twelve hours after commencement of fever, ^ c.c. taken on the second 
day, and 1 c.c. taken twenty-seven and a half hours after commencement of fever 
all caused attacks of the fever. 
In these papers the authors compare the nature of the fever to that of malaria 
partly because of the incubatory period of ten days or more necessary in the gnat; 
this, indeed, would be equally essential for a gnat inoculation of bacterial parasites, 
provided that the inoculation were not simply due to contaminated biting parts, which 
can certainly be discounted from the experiments of Finlay in so far as he was never 
able to reproduce typical yellow fever in his cases. It is only natural to suppose that 
a bacterium must also be allowed the time element in order to multiply sufficiently 
to be able to give an infecting dose whether the organism passes directly or 
indirectly into the ejecting apparatus of the gnat. Again the direct transference of 
blood from patient to experimental individual was tried because (II) ' It seemed to 
us that yellow fever, like the several types of malarial fever, might be induced by 
the injection of blood taken from the general circulation of a patient suffering with 
this disease.' This, though undoubtedly true of the animal parasite of malaria, is 
also possible in the case of bacterial parasites, as is a common laboratory experience 
when direct inoculations are made from one animal to another. 
In experiments with the transference of bacterial parasites by means of biting 
* More recently, according to the daily press, some fatal results have occurred : details as yet are wanting. 
