42

    The results of the blood examinations made in this series of cases may be
tabulated thus :—

    Now, these 68 cases had been diagnosed as kala azar before blood examinations
were made, and I have no doubt that all were true cases of the disease.
I believe, therefore, we are justified in concluding that the disease. known as
kala azar is always associated with the presence of the so-called Leishman-
Donovan parasites. Sometimes (according to the above results in about 10
per cent. of cases)* it is associated in addition with the presence of malaria
parasites or pigment, and very often it is associated in addition with the
presence of ankylostomes: doubtless other parasites are also present in many
cases.

    The problem for solution is, which of these parasites, if any, is the cause of
kala azar ?

    It will be remembered that same years ago one observer, who found
ankylostomes in every case examined, regarded this parasite as the cause of the
disease; and a few years later another observer, who found evidence of malaria
in every case examined, thought that the malaria parasite must be the cause: so
now that in the disease yet another parasite has been found, it behoves us to
examine with some care the evidence concerning its causal relationship. The
finding of the Leishman-Donovan parasite in a number of cases—and this, I
believe, is the sole ground upon which many observers base their opinion that
this parasite is the cause of the disease—is in itself, of course, no more a proof
of its causal relationship to the disease than is, let us say, the finding of
ankylostomes or of malaria parasites in a number of cases a proof that the
disease is due to either of these organisms. In a country like Assam, where a
large proportion of the population harbour parasites of several kinds, the finding
of any particular one in a patient suffering from some disease affords at the most
a probability that it bears a relation to some of the signs and symptoms present.

    But there are other reasons than its presence in every case for the opinion
that the Leishman-Donovan parasite is the cause of kala azar, and, so far as my
experience enables me to do so, I shall summarize them as follows :—

    (1) Kala azar is not due to the presence of the Ankylostomum duodenale.
This is agreed upon by all observers.

* Nearly all the patients seen in hospitals had been treated more or less vigorously with quinine ;
if they are excluded, the percentage is between 14 and 15.