9
powers the stomach tissues or their contents, separately ; or, if we wish, we
can wash away the latter by irrigation with water or weak stains, and study
the tissues alone, unstained or stained.
In the case of the mosquito fed on the healthy sparrow we shall find that
the contents consist of blood from which most of the serum has been abstract-
ed, leaving the red and white corpuscles crowded together. What serum re-
mains is densely coloured with exuded haemoglobin, in the midst of which the
white lencocytes, still living, can easily be distinguished. On examining the
tissues we find the cavity still containing traces of haemoglobin-stained serum
and perhaps a few lencocytes and red corpuscles ; but of course, neither the
tissues nor the cavity show any sign of the characteristic pigment of proteo-
soma or halteridium.
Taking, however, an insect fed on blood containing gymnosporidia,
whether hæmamœba, proteosoma, or halteridium, we shall find in the contents,
besides the condition of the blood just described, not only traces of these para-
sites, but also entire parasites still enclosed in the corpuscles, or lying free in
the yellow serum. In some of these the pigment is still oscillating. If filariæ
or trypanosomes be present, some will be found living, others dead.
I will for the present make no attempt to describe further the condition of
the parasites on this day, though the subject is one of the highest interest
(Section IV, paragraph 1). I have thought it best to forego the study for the
time, partly for this very reason, partly because the differential experiments
noted above have necessitated the insects being reserved to a later stage at
which the presence or absence of the pigmented cells becomes determinable
with certainty, and partly because the enquiry was not absolutely necessary from
a practical point of view, since an older development of the parasites had al-
ready been discovered. I will then pass at once to a study of the appearances
of the second day.
Second day—Monday.—The blood in the cavity of the stomach is still
further disintegrated. Early in the day we can indeed often distinguish a few
red corpuscles and some rounded and dead lencocytes, but later on, as a rule,
even these disappear, and the contents consist of a fairly homogeneous reddish-
black mass of multitudes of granules with brownian (?) movement. It should be
noted, however, that the temperature of the air seems to have an appreciable
effect on the period of these changes. Sometimes as early as the morning of
this day, but more generally towards the afternoon, the stomach pours almost
its entire contents into the intestine, which in its turn shortly evacuates them.
From this point the alimentary canal becomes practically empty, but for a few
traces of the meal, and the insect is ready to feed again. Meanwhile the eggs
have been developing apace and the ovaries now appear as two thick yellow
masses loosely attached to the alimentary apparatus and to the terminal
segment.
Examining insects fed on blood infected with any of the pigmented gym-
nosporidia, we shall generally still find in the stomach contenis some distinct
traces of the parasites amongst the granular mass of the disintegrated blood.
These traces consist either (a) of small clusters of pigment, (b) of scattered
pigment granules, or (c) early during this day, of pigment contained in a
yellowish, hyaline cell, the remains of the entire dead gymnosporidium. Pigment
may also be seen in the dead lencocytes. Filariæ, if present, are dead.
If examining the tissues of the stomach in grey mosquitos fed on blood
containing crescents, halteridium or immature proteosoma, after the contents have