624 
Insects and Disease 
never found in insects of the same species when fed on healthy birds or on 
birds containing the other parasite, called Hcemamosba danilewskii. 
“ It will be evident that this fact was the crucial test both as regards the 
parastic nature of these cells and as regards their development from the 
hsemocytozoa of the birds; and it was not accepted by me without very close 
and laborious experiment. The actual results obtained were as follows: 
“Out of 245 Culex jatigans fed on birds containing IT. relida 178, or 72 
per cent., contained ‘pigmented cells.’ But, out of 41 Culex jatigans 
fed on a man containing crescentic gametocytes, 5 on a man containing imma¬ 
ture tertian parasites, 154 on birds containing H. danilewskii , 25 on healthy 
sparrows, and 24 on birds with immature H. relicta —or a total of 249 insects,, 
all carefully examined—not one contained a single ‘pigmented cell.’ 
“ Another experiment was as follows: Three sparrows, one containing 
no parasites, another containing a moderate number of H. relicta , and the 
third containing numerous H. relicta , were placed in separate cages within 
three separate mosquito-curtains. A number of Culex jatigans , all bred 
simultaneously from larvae in the same breeding-bottle, were now liberated 
on the same evening partly within the first mosquito-netting, partly within 
the second, and partly within the third. Next morning many of these gnats 
were found to have fed themselves on the birds during the night. Ten of 
each left of gnats were dissected after a few days, with the following result: 
“The ten gnats fed on the healthy sparrow contained no ‘pigmented 
cells.’ The ten gnats fed on the sparrow with a moderate number of para¬ 
sites were found to contain altogether 202 ‘pigmented cells,’ or an average 
of 29 in each gnat. The ten gnats fed on the sparrow with numerous parasites 
contained 1009 ‘pigmented cells,’ or an average of 100 cells in each gnat. 
These thirty specimens were sent to Manson in England, who made a similar 
count of the cells. 
“ I may mention one more out of several experiments of the same kind. 
A stock of Culex jatigans , all bred from the larva, were fed on the same 
night partly on two sparrows containing H. relicta , and partly on a crow 
containing H. danilewskii (placed, of course, under separate mosquito- 
nettings). Out of 23 of the former lot, 22 were found to have pigmented 
cells; while out of 16 of the latter, none had them. 
“Hence no doubt remained that the ‘pigmented cells’ really constitute 
a developmental stage in the mosquito of these parasites; and this view 
was accepted both by Laveran and Manson, to wdiom specimens had been 
sent. In June, 1898, Manson published an illustrated paper concerning 
my researches, and showed that the pigmented cells must in fact be the 
zygotes resulting from the process of fertilization discovered by MacCallum. 
‘ ‘ It remained to follow out the life-history of the zygotes. For this purpose 
it was immaterial whether I worked with the avian or the human parasites, 
