A. Porter 
33 
to occur readily when the salt solution in the preparation became 
concentrated. For observing the living organism, preparations of the 
teased gut were generally used. 
Various methods of fixation were employed, but whether osmic acid 
vapour, or absolute alcohol were employed, fixation almost always had 
the effect of causing instantaneous withdrawal of any pseudopodia, and 
the assumption of the encystment form. Corrosive sublimate-alcohol 
was better for preserving the true form of the organism. The proto¬ 
plasm of these Amoebae seemed remarkably sensitive, and apparently 
they live in a most intimate, harmonic, osmotic relation with the 
intestinal fluid of their host. Very slight changes of temperature or 
concentration of solution outside the gut, as on the slide or cover-slip, 
results in encystment. The condition that produces this result within 
the gut of the host is probably the concentration of the gut contents 
as they near the anal region. That this is the case is certain, for the 
posterior one-sixth of the gut was seen to contain semi-solid contents 
and among these the cysts were found, and voided excrement also 
contained cysts of the Amoeba. 
Occurrence of the Parasites in the Host. 
The Amoebae were first noticed in the ooze from the ruptured gut 
of a recently killed larva. An unruptured gut was then carefully 
examined and the parasites could be seen within, making their way about. 
They occur throughout the gut, except just near the mouth. The 
posterior one-sixth of the gut (rectum) contained very few moving 
forms, but cysts were present, mingled with faecal matter. Examination 
of the faeces showed that cysts of the Amoeba were present in them 
and the cysts were also found in the “castings” in the tubes of the 
larvae of the Chironomus. 
The parasites can be easily distinguished from the lymphocytes and 
wandering cells so common in insect larvae, for the Amoebae possess a 
well marked, contractile vacuole. 
General Description. 
The organism in life varies considerably in appearance at different 
times according to its various phases of movement (Figs. 1—15). The 
body of the parasite consists of an elongate, oval mass of protoplasm 
in which a nucleus and contractile vacuole can be seen (Figs. 6, 7). The 
Parasitology ii 
3 
