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THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [VII, IV
Temperature is not the only factor that is capable of modifying termites so
as to destroy the intestinal flagellates living in them. Thus if a termite is starved
for 6 days it loses one type of flagellate, Trichonympha, and if it is starved for 2
days longer it loses a second type of flagellate Leidyopsis. Further experiments
with oxygen under pressure have demonstrated that the other two types of flagel-
lates, Trichomonas and Streblomastix, can be removed by this treatment without
injury to the termites, but of course no such condition occurs in nature. However,
by the use of high temperatures starvation and oxygen under pressure, it has been
shown that termites will die in about 3 weeks if all protozoa are eliminated or
if all but Streblomastix are removed ; that they will die in about 10 weeks if both
Trichonympha and Leidyopsis are removed ; but will live on indefinitely with any
combination of flagellates if Leidyopsis are present or even with Leidyopsis alone.
Thus we have proved that the symbiosis involved in this instance is between the
termite and Leidyopsis and that the other three species are merely hitch-hikers.
Incidentally the most perfect known method of transmission of protozoa
from one host to another is exhibited by termite flagellates. The young termites
soon after they hatch from the egg are fed by their parents on what is known as
proctodeal food. This is excreta of the adults consisting of partially-digested
cellulose and many flagellates. One hundred per cent of the young termites
are therefore infected soon after they emerge from the egg and are thus supplied
with a complete collection of flagellates to digest their food for them.
Blood-inhabiting protozoa have also furnished material for experiments de-
signed to test parasite reactions to host modifications. Today I wish to use the
time at my disposal to discuss three methods of treating canary birds that have
resulted in obvious changes in infections with the bird malaria parasite Plasmo-
dium cathemerium. The first method was to modify the sugar content of the blood
by feeding the infected birds with glucose or by treating them with insulin. The
clues that led to our experiments came from several sources. Bass, in 1912,
found that the addition of sugar to the culture medium was necessary to cultivate
malaria parasites outside of the body. In 1913, Bass and Johns reported the
cultivation of the organism of human malaria in the blood of a diabetic without
the addition of sugar. Certain agents that have been found to be satisfactory
as provocatives in bringing on a relapse in malaria such as epinephrin, are known
to increase the sugar content of the blood. These facts suggested that the blood
stream can be improved as a culture medium for the growth and multiplication
of malarial parasites by the addition of sugar. According to this theory, in-
creasing the sugar content of the blood would result in an increase in the number
of parasites. Vice versa, the blood stream should be rendered less favourable than
normal as a habitat for malarial organisms, by decreasing the sugar content.
It is not necessary to give details of our experiments here. In general the data
indicate that an increase in sugar content renders the blood more favourable for
the malaria parasites ; the number of parasites becomes greater and remains so for