3
Believing as I did that these cells are derived from the gymnosporidia, I
judged from this experiment that the grey mosquito which now contained them
had fed itself on one of the birds which happened to be infected by a parasite
capable of transference to the grey species of mosquito. As all the birds had
been placed together in the same net, the question now was which of them had
the mosquito fed herself upon. This could be easily ascertained.
A number
of mosquitos of the same species had meanwhile been fed separately on the
crow and two pigeons with halteridium ; but out of 34 of these examined not
one contained pigmented cells. Hence I came to the conclusion that the
mosquito with pigmented cells had not derived them from the crow and the
two pigeons. The larks and sparrows remained.
The blood of these had not yet been carefully searched. I now found that
three of the larks and one of the sparrows contained proteosoma, Labbé, and
therefore thought it possible that the mosquito had been infected from one of
these. Accordingly, on the night of the 17th and 18th March, a number of grey
mosquitos were released on the three larks with proteosoma, and next morning
it was found that nine of these had fed themselves.
On the morning of the 2oth March, that is from 48 to 60 hours after
feeding, these nine insects were examined. Pigmented cells were found in no
less than five of them. After the long continued negative experiments with
this kind of mosquito (and indeed, I may say, after three years' doubtful attempts
to cultivate these parasites) this result was almost conclusive. It indicated, as
was surmised before, that when a certain species of mosquito is fed on blood
containing a certain species of gymnosporidia, pigmented cells are developed.
Hence it would follow, as an easy corollary, that the cells are a stage in the life-
history of the gymnosporidium in the mosquito,
It was now necessary, however, to confirm and amplify this observation, and
obtain formal proofs of the theorem, by repeating these experiments and by
studying the pigmented cells themselves. Accordingly from the 18th March
to the present date many differential experiments have been completed by
feeding grey mosquitos as follows :—
(a) On larks, sparrows and a crow with proteosoma.
(b) On crows, pigeons and other birds with halteridium only.
(c) On a lark and a sparrow with immature proteosoma only.
(d) On a healthy sparrow,
Only the insects fed on group (a) have contained pigmented cells.
I will now give a list of these experiments, dividing them into series
numbered in succession to those already recorded in paragraph I of this
section. They will be found to illustrate in a striking manner the restricted
association between the proteosoma in the birds and the pigmented cells in the
grey mosquitos, Beginning from the commencement of my employment on
special duty the series are as follows.
3. List of Recent Results.
Series 10. Out of 41 grey mosquitos fed on a case of crescents (4th to
21st March), none contained pigmented cells.
Senes II.—Out of 15 dark, greenish dappled-winged mosquitos fed on
a case of crescents, none contained pigmented cells. These insects were
probably of the same genus, but not of the same species as those employed in
Series 5, in which pigmented cells were found after feeding on blood containing
crescents (4th to 21st March).