YELLOW FEVER EXPEDITION 
Negative Cases 
505 
Number 
Species of 
gnat 
Date of fever of 
source 
Days of 
incubation in 
gnat 
Total 
gnat bites 
I (II) 
S. fasciata 
5th day, severe 
I I & 14 
S. fasciata 
3rd da)', severe 
6 & 9 
2 
2 (11) 
S. fasciata 
3rd day, moderate 
12* 
2nd day, well marked 
iot 
3rd day 
, 5 * 
2nd day 
»3t 
4 
4 (H) 
S. fasciata 
2nd day, severe 
10* 
2nd day 
13* 
2nd day 
17* 
3rd day, fatal 
1 2 
4 
5 (II) 
S. fasciata 
3rd day, well marked 
12* 
3rd day 
15* 
3rd day, well marked 
18 
3rd day, well marked 
18 
4 
ix (III, p. 18) 
S. fasciata 
1 day 
22 
1 2 
XX (III) 
C. fungens 
? 
19 
5 
Leaving the last two out of account, and taking the twelve successful inoculations, 
this gives a proportion of failure in 25 per cent. From this we may take it that 
there is not always a sufficient number of the parasitic agents in the blood 01 a 
patient on the second or third days to infect a gnat, so that it becomes able to pass it 
on when feeding on a susceptible person. This suggests the conclusion that the 
parasite would not be discoverable in an ordinary pair of coverglass films, supposing 
that one, or quite a few, are sufficient to cause infection of the gnat, for the amount 
of blood, etc., taken by the gnat is greater than that used for such films. Hence, 
perhaps, the examination of plain blood films has been hitherto without avail. 
The commencement of an attack of yellow lever and the time of infection has 
often been said to be during the night. In view of this the report of Major Reed 
(III, p. 21) says ' If the hour of inoculation in all of our cases should have taken place 
at about sunset, then with the same period of incubation, seven, or 43 per cent., would 
