12
On examining control insects fed on blood containing crescents and
halteridium, no pigmented cells will be seen.
In those fed on blood with mature proteosoma we shall find them in various
numbers, and occupying exactly the same position as on the second day. They
are, however, markedly larger and their outline is rounder ;. at the same time, it
will be noted that they belong to one or the other of two varieties—they are
either vacuolated or hyaline (Plates IV and V).
The vacuolated cells have generally a very marked and rather thick outline.
They contain vacuoles and granules similar to those found in the larger cells of
the previous day, but these are more numerous and more closely packed within
the capsule. Some of the vacuoles are much larger than before, often reaching
a diameter of 6 μ and even more ; while the granules retain their former dimen-
sions. Altogether these cells present a very substantial appearance and are at
once distinguishable, even when out of focus, from the delicate tissues of the
stomach.
The hyaline cells consist of a fine, sharp outline containing a perfectly clear
plasma, in which however we can just discern some very faint vacuoles toward
the centre of the cell.
In both varieties alike, the pigment tends to accumulate round and outside
one or two large vacuoles, though scattered granules are generally present.
The number of granules is, moreover, less than on the previous day, and their
size is perhaps smaller.
In some mosquitos nearly all the cells belong either to the one or the other
variety, and that at the moment when the specimen is first made; in others the
two varieties are found side by side. I have frequently observed that hyaline
cells have become vacuolated after ten or twenty minutes, but nave never been
so fortunate as actually to. witness the change. This might lead one to infer
that the latter are a post mortem form of the former, were it not that both
varieties may certainly be observed immediately after dissection and that perfect
hyaline cells occur in insects which have been dead some hours. I can therefore
offer no conjecture as to the nature of these differences in appearance between
the two varieties.
As the third day advances, the pigment continues to decrease in amount ;
while, in some of the largest cells, a new element begins to appear, namely, a
few bright refractive points scattered through the plasma. I take these to be
minute globules of an oily nature comparable to those described by Leukart in
coccidium oviforme ; and shall in future denote them as such, although I am by
no means confident in my opinion.
Meanwhile, the cells continue rapidly to grow in size until at the end of
the day (72 hours) they may reach a major diameter which I put down at 30 μ
in the largest cells. The average sizes for the day, however, lie between
16 μ and 25 μ, while cells so small as even 10 μ may occasionally be seen
indeed, I have often noticed great variations of size on this day.
Fourth day—Wednesday·.—-The cells have grown still more, and on the
evening of this day (96 hours) may reach 40 μ in diameter; The averages lie
between 25 μ and 35 μ, and I think that there is more uniformity of dimen
sions on this day than on the preceding one (Plate I, figures 13, 16; Plate
VI).
If the insect examined be one which has survived to this day without refeed-
ing, the cells may, Γ think, be stunted in growth and may scarcely exceed those
of the third day in. size.