6
on the two sparrows with numerous and moderate proteosoma put together,
and partly on a young crow with halteridium. Out of 23 of the former 22 had
pigmented cells ; while out of 16 of the latter none had them.
Crows gave interesting results. They are subject both to hálteridium
and to proteosoma ; but I have found only one crow with the latter. In that
one, however, the typical round sporulating form of proteosoma was observed.
For some time the feeding experiments, for which I used various combinations
of two or three crows at a time, had been giving contrary results ; at one time
positive, at another negative. On referring to my notes it was seen that the
positive experiments occurred only when the crow with proteosoma had been
present in the net (Series 6).
According to Manson's theory, infection of mosquitos should not take place
unless flagellate bodies are present in the blood of the subject. Some ex-
periments were designed to test this by means of feeding grey mosquitos on
birds with immature proteosoma. No pigmented cells were found (Series 28
and 29). Further observations are, however, required in this connection.
Some of the experiments, namely, those on birds known to contain ripe
proteosoma (Series 24, 25 and 26) yielded almost invariably positive results,
namely, 76 mosquitos with pigmented cells out of 81 fed, or 94 per cent.
Hence I think it quite possible that in future experiments made on carefully
selected subjects, positive results may be obtained in 100 per cent. of the
mosquitos,
An explanation may be required as to why insects were so often fed on
groups of birds. The reasons are that wild birds become frightened and restless
if caged all night alone, and that more mosquitos can be fed at once on several
birds than on one, since, as I have actually experienced, small birds can be killed
from loss of blood abstracted by too many mosquitos, Moreover, according to
theory, the presence of flagellate bodies is necessary to infection of the second
host ; so that, especially when we have not had time to make a previous exhaustive
study of the subjects' blood, the chances of causing infection are increased by
using several birds at once instead of one. For more exact work, however
single feeding must be adopted.
6. Deductions from the Feeding Experiments. — There can be no question,
then, that the pigmented cells are derived directly from the proteosoma. We
can, however, already go further. The fact that similar cells were not found in
control insects of the same species fed on blood containing other gymnosporidia
will convince any one acquainted with parasitology that we are not dealing
here with any mere physiological absorption of pigment by the stomach cells
of the mosquito but with a vital phenomenon in the life-history of proteosoma,
with a remarkable transformation by which the pigmented parasite in the
blood of the bird becomes a pigmented parasite of some kind in the stomach
tissues of the mosquito. It remains to add another mass of evidence to the
same effect, deduced from the location, structure and growth of the pigmented
cells in the mosquito ; and to show how they undergo a development similar to
that of filaria-embryos in the same host. Some details of the technique are
however, required as a preliminary.
III.— The structure and development of the Proteosoma-Coccidia in
Grey Mosquitos.
I. Technique.—Mosquitos are obtained by catching the larvæ, or better
the pupæ, in pots of water, drains, and puddles. These are placed in wide-