58
Para. 31
one or another of them in a patient can affect the question of the disappearance
of the parasites and the black pigment from his system.
In one very important particular. We know that when, from any cause,
an attack of fever due to the quartan or tertian parasites ceases, the organisms
disappear, apparently, from the blood in a day or two. This is not exactly the
case with the æstivo-autumnal variety ; here the fever-producing forms dis-
appear as in the other cases, but a crop of crescents is produced which
remains and is found in the blood for weeks or even months after the subsidence
of the fever, but which seems to cause no symptoms. In the former case, with
the partial or complete collapse of the invasion, the black pigment must cease,
partially or completely, to be deposited in the organs. In the latter case, how-
ever, the crescents remain, as I have said, for a long time, and as they die one
by one their pigment, which is always profuse, continues to find its way to
those organs.
Now, we may conjecture that the elimination of black pigment must go
on continuously with its deposition. I have already cited authority to show
that it may be completely eliminated in a few months. As a matter of fact we
often find less pigment in the organs of long infected birds than can be produced
by a few generations of the parasites present. Bignami has studied these
processes with great care and describes the course of elimination. Unfortun-
ately I have not obtained his work yet, and therefore cannot quote from it ; but
Thayer gives an excellent summary [27, p. 225]. The period of elimination
is, of course, not exactly definable, as it depends on the amount of deposition ; but
it probably may not, in some cases, extend beyond a few months. (See case 17
for instance).
In æstivo-autumnal infections, then, we may expect to find both parasites
(crescents and their derivations) in the blood, and melanin in the organs, longer
after each conflagration of fever, and perhaps after the final extinction of the
parasites, than in the case of quartan and tertian infections. (It should, of
course, be noted that crescents are practically encysted organisms, probably
serving a purpose outside the host, and, when once formed, little amenable to the
influences of immunity.) It follows, therefore, that in quartan and tertian
infections occurring among aboriginal populations of malarious localities, the con-
dition found by me in kala-azar, namely, one of absence of parasites and melanin,
must be arrived at sooner than in æstivo-autumnal infections.
An interesting illustration of these observations is given by Captain Harold
Brown's study of kala-dukh in the Purnea District [16], already referred to in
paragraphs 9 and 13. He found parasites in 45 out of 50 cases ; but in 43 out
of those 45 crescents were present. It is clear, then, that these were cases of
æstivo-autumnal infection. In my 75 cases, crescents were observed only in
three. Hence, on the supposition that kala-azar in Assam is paludism, we
may explain the discrepancy between Brown's results and mine, and at the
same time give one good reason for the absence of parasites and melanin in the
later cases by attributing them to a quartan or tertian infection. I may add
that Rogers also failed to find crescents in his cases. In a letter to me
Captain Brown adds that his investigations were made in April 1898, and
remarks —" As a rule, the parasites were few except in the two cases that were
noted as having quartan ague, in whom they were decidedly numerous. In the
more recent cases, they were more numerous than in the chronic ones
when, at times, it required patient observation to detect them." Crescents as
well as " large and small pigmented bodies " were present in the two quartan
cases ; which, therefore, might have been mixed infections. Unfortunately,
Brown does not specify the exact nature of the "pigmented bodies," which he
refers to in most of his cases, and never refers to unpigmented amœbulæ, which
are the fever-producing forms of the crescent-bearing (æstivo-autumnal)
species. I gather, then, that most of his pigmented bodies were crescent-derived
spheres, and that kala-dukh in Purnea is essentially æstivo-autumnal paludism.
It is possible to imagine that had the crescents been, so to speak, removed
from Brown's cases, they would have exhibited the absence of parasites and
melanin observed by me in kala-azar.*
* Note.—It is also possible that certain local varieties of æstivo-autumnal parasite may produce very few
crescents. Thus, Dr. Daniels informs me that in British Guiana, though the species of parasite is æstivo-
autumnal, he finds comparatively few crescents. He expressed his surprise at the number of those bodies in four
Calcutta oases, although from my experience I considered them to be not at all remarkably numerous. It
should he noted also that in British. Guiana it is the rule to find enlarged spleens without melanin—so that
the fevers there and at Nowgong seem to accord in several particulars, namely, the paucity of crescents, the
frequent absence of melanin, and the low fever. See Appendix A 6.