10

II

PREVIOUS observers attempted to solve the problem set forth in the preceding
section by comparing the clinical signs and symptoms of cases diagnosed
as kala azar by medical men in Assam, with the clinical signs and symptoms
which they believed to be characteristic of malarial fever. But before any one is
entitled to use this method for the purpose stated, he must prove the truth of two
suppositions: one is that in Assam cases of kala azar are diagnosed accurately ;
the other that he has nothing more to learn regarding the signs and symptoms
of malarial fever as it occurs among natives of India. And even if the method
is not condemned by the difficulty of converting these two suppositions into
truths, it must be admitted that, for the purpose of fathoming the nature of a
disease presumably new to science, the comparison of its clinical signs and
symptoms with those of diseases already known, is a method of investigation
to be avoided; for it is obvious that the signs and symptoms of two entirely
different diseases may be exceedingly similar. In employing the method
of investigation described in the preceding section, it was unnecessary to be
able to diagnose cases of the disease known to natives of Assam by the term
kala azar, nor was it necessary to know the signs and symptoms of malarial
fever as it occurs among natives of that country: it was necessary only to select
certain places in which the presence of a disease known as kala azar was
established, and certain other places in which a disease known by this name did
not occur, and to ascertain whether these places were, or were not, malarious.
From the results of the investigation carried out on these lines I was convinced
that, whatever the disease known as kala azar is, it is not a form of malarial fever.

        Thus far we were able to proceed without studying individual cases. But in
order that we may be in a position to form an opinion as to what the disease is,
rather than what it is not, a study of individual cases is necessary; and for this
purpose we must be able to diagnose them accurately. To this matter, therefore,
I propose to devote the present section.

        If kala azar is not a form of malarial fever, it is evident that in India there
are two chief diseases (namely, malarial fever and kala azar) in which fever and
enlargement of the spleen are prominent signs. In the Punjab I could find only
one of these diseases (namely, malarial fever),* but the results to be detailed in
this section will show that in Assam both occur. The apparent difficulty of
distinguishing between them is to be explained, I believe, by the truth that

        * See Scientific Memoirs by Officers of the Medical and Sanitary Departments of the Government of
India, New Series, No. 13.