61
Paras. 32 & 33
the ferruginous deposits ; but many cases of enlarged spleen occur in which
there is none of either. It may, perhaps, be due to, or at least initiated by, the
black pigment, or by a toxin secreted by the parasites ; but, here again, there is
evidence to show that the organs continue to enlarge without the presence of
melanin, showing that the malarial invasion is already a thing of the past.
Lastly, it may be due, as Manson suggests, and as the concurrence of the low
fever may encourage us to believe, to a secondary bacterial infection ; or perhaps
it may be connected with the establishment of immunity, which is possibly part
of the function of these organs —they may enlarge in the effort of producing
the "internal secretion" of an antitoxin.
I have not laid much stress either on the yellow pigment or the iron,
chiefly because our knowledge of both is very imperfect. The fact, however, that
they are so frequently present in kala-azar appears to limit the malady to the
small group of hæmolytic diseases, and is, therefore, valuable evidence in favour
of the malaria theory. But I should add that Dr. Daniels is of opinion that
both are produced in ankylostomiasis—Appendix A 6.
I will conclude this long discussion by formally considering the final
question which still requires an answer—that of paragraph 28.—What proof
have we that the condition of enlargement of the spleen and liver without
black pigmentation, found by me in some of the cases in Nowgong, is due to
malaria at all, and not to some quite different cause ?
I have suggested an explanation of the phenomenon frequently already—
that the parasites become extinct and the pigment is eliminated, leaving the
organs in the condition referred to.
But since the melanin is absent, how be certain that it was ever there at all ?
Daniels finds the same condition in British Guiana, and it probably exists
widely elsewhere. May it not be due to a non-malarial disease which,
however, has been mistaken for malaria ?
On the whole, I think it is impossible to admit this, for the following
reasons : —
1. The enlargement of the organs in Nowgong and British Guiana is
an endemic enlargement. Now this, in general experience, is found only
in malarious, even only in very malarious, localities.
2. The organs are seen to enlarge under our eyes in acute cases of
paludism in which the parasites are actually present ; and the parasites may
often still be found when a considerable degree of enlargement has been reached.
3. The structure of the organs in cases in which the melanin is absent
is identical with that in the cases where it is present ; and cases of the former
exist side by side with those of the latter, being like them in every respect
save in that of the pigment.
4. All the cases give the same history of the typical fever and other
symptoms of paludism.
There is, then, no reason for supposing that the cases without black
pigment differ in nature from those with it, and no likelihood that this is the
case. On the other hand it is easy to explain the absence of the pigment
simply on the ground that it has been eliminated shortly after the extinction
of the parasites.
Practically the only argument which can invalidate this reasoning is to the
effect that the melanin once deposited, must remain permanently in the organs
for at least a year or two in every case. I know of no grounds for such an
assertion. It is even doubtful whether it can remain for long in any case.
If melanin can be eliminated in one case it can probably be eliminated
in all, or at least in a percentage. The time required for its elimination must
depend, cæteris paribus, on the amount of the deposit.
In short, before we can accept that the condition under reference is not due
to malaria we must be in a position to prove that melanin cannot be eliminated
at all except after some years.
33. Summary of the Discussion.—The objections to the malarial theory
of kala-azar were stated in paragraph 22. They were (1) the high death-rate of
the disease and its intractability to quinine ; (2) the absence of parasites and
pigment and the existence of low fever in the later stages ; and (3) its
communicability.
The first objections (1) were shown not to be serious ones (paragraph 24).