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       So far as my experience enables me to do so, I may therefore summarize
the evidence against the Leishman-Donovan parasite being the cause of kala
azar somewhat as follows:—

       (1) Although I found the Leishman-Donovan parasite in 67 out of 68 cases
of kala azar, this finding, taken alone, affords no proof that the parasite is the
cause of the disease. Let us suppose, for the purpose of illustrating this truth,
that I had found the malaria parasite in 50 successive cases—and it is possible
that, if one were permitted to select the cases carefully, such a result could be
obtained—it would afford no proof that the malaria parasite is the cause of the
disease, because by methods which are unimpeachable I have shown that kala azar
is not due to this parasite. (See Section I.)

       (2) Although the Leishman-Donovan parasite is present in every case of
kala azar—a disease in which enlargement of the spleen, fever, and wasting
are prominent features—it (or a parasite indistinguishable from it) is also
present in every case of Oriental Sore—a mild local disease in which constitu-
tional signs and symptoms are absent.

       (3) Although the parasite is abundantly present in parts of India where kala
azar is prevalent, it (or a parasite indistinguishable from it) is also present in parts
of India where this disease is unknown. If it produces kala azar in one part of
India, why not in another ? Obviously some other factor than the parasite is
necessary for the production of this disease.

       (4) Even when enormous numbers of parasites indistinguishable from the
Leishman-Donovan parasite are present for many months in ulcers on the
bodies of persons, no disease like kala azar results.

       (5) There is no evidence to prove that the fever observed in cases of kala
azar is due to the presence of the parasites; the fever in kala azar bears no
relation either to the number or condition of the parasites present: and there is
evidence that parasites indistinguishable from the Leishman-Donovan parasites
(namely, the parasites of Oriental Sore) are incapable of producing fever. If the
parasites found in kala azar do not cause one of the chief, and earliest, signs
of the disease, is it not reasonable to assume that they do not cause the other
signs and symptoms present ?

       (6) Until kala azar has been produced experimentally by some form or other
of the parasite, it will be necessary, before the causal relationship of the parasite
to the disease is established on sure grounds, to prove that every other kind
of parasite which has been found in the past, or may be found in the future, in
patients suffering from kala azar has no causal relationship to the disease.
This has already been done with regard to the malaria parasite and the
Ankylostomum duodenale, but it is not impossible that other parasites, not yet
discovered, may have some share in the production of the disease. So far as