5
Seríes 33.—Out of a few lice and horse-flies (Tabanus) fed on pigeons with
halteridium (May), pigmented cells have not been found in any.
4. Abstract of Recent Experiments with Grey Mosquitos.—Thus we
find:—
Out of 245 grey mosquitos fed on birds with proteosoma, 178, or 72 per
cent., contained pigmented cells.
Out of 41 grey mosquitos fed on a man with crescents, 5 on a case o£
immature tertian parasites, 154 on birds with halteridium, 25 on a
healthy sparrow, and 24 on birds with immature proteosoma, or a
total of 249 insects altogether, not one contained a single pigmented
cell.
5. Some Particular Experiments.—These experiments, then, are sufficiently
decisive ; it remains to discuss some of them more particularly. After the pig-
mented cells had been found in large numbers of insects fed on birds, with pro-
teosoma (Series 15, 16 and 17), it was thought time to commence some formal
control experiments. Three fresh sparrows had been examined on the 23rd
March after a day of fatiguing work with the oil-immersion lens, and no parasites
were observed in them. A stock of mosquitos fed on them, however, showed pig-
mented cells in 6 out of 18 insects (Series 19). The birds were examined again,
more carefully, when it was found that two out of the three- did contain proteosoma.
after all. Indeed, when re-examined, one contained large numbers (namely,
about 1 parasite to 50 corpuscles), the second contained a moderate number
(about 1 parasite to 1,000 corpuscles), while in the third no parasites at all could
be found. I now placed these three birds in separate cages, and put each cage
within a separate mosquito-netting. A number of mosquitos caught in the larval
stage in the same part of the same drain and hatched out in the same breeding,
bottle were now liberated at the same time (2nd April), partly on the first bird,
partly on the second, and partly on the third. Next morning those which had
bitten each bird were confined separately in test-tubes. On examination (Series
24, 25 and 26) it was found that out of 20 mosquitos fed at the time on, the
sparrow with many parasites, and out of the same number fed on, the sparrow
with a moderate number, all without exception, namely, 40, contained pigmented
cells ; while out of 15 insects fed on the sparrow with no parasites, not one con-
tained any pigmented cells. Moreover, the stomachs of ten insects of each of-
these series were preserved and the number of pigmented cells in each series
counted by means of a low power. The result was as follows :—
(a) Ten mosquitos fed on the sparrow with numerous proteosoma con-
tained 1,009 pigmented cells, or an average of 101 each.
(b) Ten mosquitos fed on the sparrow with moderate proteosoma con-
tained 292 pigmented cells, or an average of 29 each.
(c) Ten mosquitos fed on the sparrow with no proteosoma contained no
pigmented cells.
I could not afford time to count with the oil-immersion lens. Had I done
so, the number of cells found would doubtless have been larger. One of the
mosquitos of series (a) contained no less than 445 of the cells. This expeiiment
was repeated later with a few mosquitos and similar results were obtained.
Numerous experiments of the same kind were now carried on, by feeding;
mosquitos out of the same breeding bottle at the same time, (a) on birds with
proteosoma, (b) on birds with halteridium. A large percentage of the former
always possessed pigmented cells ; none of the latter ever did so. For in
stance, on. the night of the 12.th. to 13th April, a stock of mosquitos was fed party
Bi