66
Para. 37
On the other hand, I venture to state definitely that proteosoma of birds
is communicable. Owing to the great similarity between the avian and human
parasites, and to the fact that research in regard to the latter has already
yielded results identical to a certain distance with those obtained in respect to the
former, it becomes almost impossible to avoid a like conclusion for paludism.
In making this statement I do not wish to be misunderstood. The disease
cannot be directly communicable like scabies or venereal disease ; but rather in-
directly like rabies, filariasis, Texas cattle-fever, or nagana. Accepting the
analogy with proteosoma, communication will require that the proper species of
mosquito, or perhaps other insect, be present, and also that the particular insect
has lived for a week or more, after biting the subject, before it can infect the
object. Now, mosquitoes have many enemies—spiders, bats, strong winds, while,
so far as I can ascertain, the species of insect which commonly infest our houses
in India, and the larvæ of which live in pots of water, garden cisterns, and so on,
cannot carry human malaria. Hence it follows that very particular conditions
must be present before communication can be established.
Such conditions are not likely to exist to any great extent in our hospitals
and in the houses of Europeans. In the Nowgong District, however, the houses
of the poor are placed in the most favourable situation in this respect. Situated
on the ground, surrounded by pools of stagnant water, and made generally of
open matting work, they permit the ingress of hordes of mosquitoes of numerous
species which, day and night, bite the half-naked bodies of the inmates, and
when gorged, sleep in the dark, damp corners of the roof, returning after
digestion for another meal, and living on in the same house probably for weeks
and perhaps even months.
It will be perceived that a mosquito of the proper species existing in such
a situation may carry the infection from any sick person who has entered the
house to many of the other inmates in turn ; and that, moreover, as suggested
in paragraph 30, most of the insects there may shortly become infected and
may repeat the dose of malaria nightly to the unfortunate inhabitants until all
suffer from a frightful condition of parasitism. Still further, many of the infected
insects may escape to neighbouring houses and afflict the occupants of these in
a similar manner. Finally, when a patient so attacked removes to another
village or hamlet where the mosquitoes of the proper species exist, he will start
an epidemic of the same nature.
It should also be remembered that, according to my observations on proteo-
soma [2], very few sparrows bitten by infected mosquitoes ever escaped infection,
and that nearly all of them suffered from the severest invasions I have ever
witnessed.
Some other attempts at the solution of the malaria problem should be
mentioned here. Sakharov, Rosenbach, Blumer, Hamburger and Mitchell—
see [27, p. 27]—have kept the parasites alive in leeches. MacCallum found his
motile vermicules in the intestine of crows(?) with halteridium ; but these birds
suffered from echinostomes [39, p. 130].
Rogers, to whom we are so largely indebted for his work on kala-azar and
especially for his boldness in declaring the communicability of paludism, does
not, however, I think, afford a very satisfactory explanation of this phenomenon.
He attributes it, in the case of kala-azar, to a heightened virulence of the
parasites of malaria in that disease, and considers the path of infection to be
by way of the lungs. It is little likely, in the case of an animal parasite, that
any increment of virulence should suffice to change its mode of propagation ;
and he cites no experiments to prove communication by the lungs.
On the whole, I think that the mosquito theory of Manson will suffice
to explain the whole epidemiology of malaria, and believe that it may be
accepted as established, although many details remain to be discovered.*
* Note.— Just as I conclude this paragraph, I have heard, by the kindness of Dr. Edmonston Charles of
Pome, that Grassi, Bignami, and Bastianelli have succeeded in confirming my results regarding the cultivation
of the æstivo-autumnal parasite. They have produced the " pigmented cells " in the Italian mosquito called
Anophelos claviger, Fabr., or Anophelos maculipermis, Meig. Dr. Charles has sent to me two specimens of this
mosquito given him by Grassi. It is, however, different from my " dappled-winged " mosquito. These ob-
servers, writing in collaboration, have already published a preliminary note on the subject (40).