50
Paras. 28 & 29
This question is of the greatest importance, not only as regards kala-azar,
but as regards malaria in general ; and not only in respect to academical
theories, but in respect to the actual treatment of cases. It can be finally dealt
with only by giving a reasonable theoretical explanation of the phenomenon.
I will now attempt this explanation. It will, I fear, involve some hypo-
thetical matter, but, I trust, may still be of sufficient interest to atone for its
prolixity.
What, precisely, have we to consider ?
The superficial explanation of the phenomenon—that in the condition
referred to the parasitic invasion has died out and the melanin been eliminated,
leaving, however, a diseased state of the organs which accounts for the secondary
fever—has already been mooted in paragraph 14. It is now necessary to go
deeper. We must enquire, what is likely to cause the disappearance of the
parasites and melanin ? Under what conditions is this disappearance likely to
be most speedy ? What influence is likely to be exerted in regard to the
disappearance by the species of parasite concerned ? How explain the low fever
and other details ?
29.—Gradual Extinction of the Parasitic Invasion.—The depend-
ence of the typical malarial intermittent and remittent fevers on the parasites
of the red blood corpuscle has long been recognised as being practically an
absolute certainty—so much so, that recent writers do not even take the
trouble to discuss it.
The movement, sporulation and other cytological
characters of those bodies, their close analogy with a whole series of similar
intra-corpuscular organisms in some lower animals, and, I may now add,
the cultivation of one of these in mosquitoes and its introduction into healthy
birds, suffice to establish beyond all doubt their parasitic nature. Their causal
relationship to the early febrile and some other incidents of paludism is manifest
from the facts that the typical melanin found in the disease is produced in their
interior and that the accessions of fever depend upon phases in their life-history.
But paludism does not consist merely of attacks of malarial fever. A
typical untreated case—especially as seen in very malarious localities—exhibits
a long graduated series of such attacks accompanied by a profound affection of
many of the tissues of the body. The disease, properly speaking, bears less
affinity to such brief infections as those of measles or small-pox, for instance—
with their rapidly-produced individual immunity—than to such prolonged
infections as syphilis, tuberculosis, filariasis.
We are quite familiar with cases in which ague, accompanied by detectable
parasites, continues to appear from time to time in patients who have removed
for years to a non-malarious climate. For example, Major Giles, I.M.S., has
told me of a lady who still gets fever occasionally, though she has lived in
England for nineteen years after she contracted the disease.
What relationship, exactly, do all the symptoms of such a disease bear to
the parasitic invasion which we know must have caused its onset, at all events ?
Our first difficulty here lies in the following point. We know that if we
examine such a case as just noted, we shall probably find the parasites with ease
during the attacks of the typical fever ; but in the long intervals between the
attacks—when the patient appears almost or quite well—we shall probably find
nothing. We know that the parasites must continue to live in the system in
some way during all these long intervals —under what form and how ? Manson
[14, p. 7] suggests a latent phase of the parasites ; and I have sometimes thought
that this phase may be similar to the encysted stage of the parasites found in
mosquitoes. Thayer, in discussing the question [27, p. 184], says "the specific
organism must exist in some form within the economy during this long period
of time. It is hardly conceivable that it should remain in the general circula-
tion, passing through its ordinary cycle of existence, without causing any symp-
toms whatever;" and he falls back on the supposition of Bignami, that there
may be an encapsulated form.
Thayer, however, gives no reason why he finds the continuance of the
parasites in the circulation so inconceivable. The point must be closely
examined, as it is of first importance in the treatment of paludism.
In my experience of halteridium of pigeons and crows in India, I have
always found, out of some twenty birds kept under observation, that the para-
sites once present never disappear, and even remain roughly in the same