208 GNATS OR MOSQUITOES — CHAPTER VIII fastidious of Culices, though, within cantonnients, where their contents may be Httle else than rainwater, they occasionally do so. In provinces, on the other hand, where the rainfall is heavy, and especially in such tanks as lie in the line of a natural drainage depression, and are hence scoured out by heavy falls, such tanks may contain larvae ; but I doubt if they are likely to do so for any considerable portion of the year, though it is hazardous to attempt to generalise in such a matter, as exact local knowledge is alone of any value. It must be remembered in this connection that, in Lower Bengal, tanks arc largely used as sources of drinking water, and such tanks are more or less guarded from pollution, for callous as the Indian may be in this matter, there are few who would drink the water of a town tank in Northern India ; and any tank containing water that would be regarded as drinkable, even from a native point of view, would certainly form a congenial habitat for Anopheles larvae, and the improvement of municipal sanitation against malaria will be in such places proportionally difficult. Where not indispensable as sources of drinking-water, such tanks might doubtless be dealt with by the use of larvicides ; but in such places these tanks are both large and numerous, so that the expense would be a large and constant one, and we are further met with a difficulty that must be fatal to the success of all temporary, and therefore continuous measures in India — the difficulty of providing adequate intelligent supervision.
Another reason why not only cities but also smaller longinhabited sites tend to become less malarious is that the ground level is being slowly but continuously raised by the accumulation of the ruins of older buildings on which, from time to time, new buildings are raised. Often, in India, village sites are of an unknown antiquity, and in such the tortuous village streets wind their way always up hill to its centre, where often there still stands the more imposing home of the headman. The older the hamlet, the higher the hill, and some have lasted so long that the site of the hut from which it grew may now be 50 feet or more above the unbroken level of the surrounding plain. Now it is obvious
CONDITIONS INFLUENCING PREVALENCE 209 that this self-raising action must have a most beneficial effect by favouring surface drainage, and this affords us a hint that might well be taken advantage of in planning new settlements on ground reclaimed from the desert by canal irrigation ; only in place of gaining the earth by honeycombing the plain hard by with a network of foul tanks, the spoil should be taken from carefully planned drainage cuts carried along the natural lines of drainage. Surely, considering the vast outlay involved in the construction of a great canal, it should be a good investment to spend considerable though comparatively trifling sums to secure health for the colonists who come to reap the plenty brought by the fertilising water.
Such being the conditions that influence the prevalence of Mosquitoes, it may be asked whether the seasonal prevalence of these insects really corresponds with the intensity of malarial disease ? On this point the figures given by Colli are sufficiently convincing, but for many reasons it is difficult to quote statistics of corresponding value for India, though, speaking generally, no doubt can be entertained as to the fact of the coincidence, or rather consequence. The connection is, however, of a kind that is much more obvious to the working physician that to the statistician. The former well knows that, in Northern India for instance, his really troublesome malarial cases occur between the middle of August and the end of November, and that those which are admitted between January and August are mostly recurrences, generally lasting only a few days, and of a comparatively mild type.
These relapses, however, go to swell the number of admissions in months during which, in many parts of India Anopheletes are, practically speaking, as rare as the dodo ; and thus it happens that in spite of the infinite amount of labour that is wasted on the statistics that lumber the record rooms of our offices in India, we are still quite without any really reliable information as to the seasonal prevalence of malaria.
Apart from the fact that hitherto no attempt has been made to distmguish between primary and recurrent attacks, 14
210 GNATS OR MOSQUITOES — CHAPTER VIII a distinction which, it must be admitted, it would be very difficult to make in practice, the diagnosis between the various forms of pyrexial disturbance, that in India and elsewhere in the tropics are grouped together as "fever," has hitherto been made in a very loose way. No statistics as to malaria can be considered to be exact and definite in which the diagnosis is not based on the ascertained presence of the parasite in the blood, and as yet such statistics on any considerable scale are entirely wanting. No doubt in the majority of cases the symptomatic diagnosis of malaria is perfectly correct, but we are only now commencing to differentiate exactly between remittent, malarial, typhoid, and Malta fevers, and on the other hand there can be no doubt that numbers of cases of transient pyrexia, due really to digestive disturbance giving rise to the absorption of toxic materials from the bowel, and to various other causes, are returned as malaria. Such cases are very common in the dry, hot season, and in a large proportion of them certainly, the most careful examination fails to demonstrate parasites in the blood. A certain number of course are really malarial, but are recurrent attacks which, as far as my limited experience extends, appear in this part of India to be usually characterised by the presence of the small, round, unpigmented forms unaccompanied by crescents in the peripheral blood. In spite, however, of these sources of fallacy the figures at our disposal are really sufficiently conclusive for all but the most exacting.
Taking the returns of intermittent fever as the least open to diagnostic errors, we find that the last available report of the Sanitary Commissioner with the Government of India shows that in the European army the monthly admissions were as follows : —
CONDITIONS INFLUENCING PREVALENCE 211 These admissions took place on a strength of 67,697, so that roughly speaking about a quarter of the entire force suffered from malarial fever during the year. In the native army the seasonal prevalence of the disease follows a closely similar course. Bengal Punjab Madras.. Bombay ..
Hyderabad Contingent ,480 2,417 1,704 044 65t) 1,167 1,532 1,596 2,112 696 802 124 1,339 '658 543 94 8,247 11,847 5,571 5,882 941,077 2,419] 33,434 ■ This on a strength of 128,529, and again it will be seen that roughly a quarter of the strength suffered from malaria. Our European and native armies in India are not strictly comparable, as the latter is a long service force, necessarily composed of men, older and more seasoned to soldiering than their European comrades ; but in spite of this, while rather less than a quarter of the former suffered, the latter did so in the proportion of rather more than a quarter. Something of the difference is doubtless due to the more sanitary tendencies of European personal habits ; but making all such allowances, it must be admitted that if the native has acquired any immunity he has done so to so small an extent that it is a factor of too trivial importance to be worthy of practical consideration. It is further noteworthy that in specially malarious districts, such as the Bengal and Orissa group of stations, where the relatively greater preponderance of genuinely malarious cases tends to minimise the fallacy of included cases of diseases simulating malaria, the seasonal variations in the intensity of maiaria are much better shown than in less malarious places. In all stations where the seasonal prevalence of Mosquitoes has been made the subject of careful investigation, the period of greatest intensity of malaria has been found
212 GNATS OR MOSQUITOES— CHAPTER VIII to coincide with that of the greatest prevalence of Anopheletes.
As a striking example of this I may instance that writing to one of my numerous correspondents, Lieut. Glen Liston, I.M.S., who is quartered at Ellichpur in the Berars, to ask him if there was any reason to believe that one of the methods of securing permanence of the species might be the survival of retarded larvae, he replied that there. Anopheles was breeding already at the date of writing (January), and sent me numbers of specimens including some in tubes, one of which actually reached me alive. Now it is a curious fact that in the above-quoted table, Ellichpur is one of the few stations in which the largest number of malarial admissions takes place in January, the monthly admissions being 31, 12, 10, 3, 7, 2, 8, 14, 9, 29, 21, 15; total im.
In Indian jails the figures are closely similar. Out of an average strength of 110,016, there were 37,776 admissions for intermittent and 734 for remittent fever, the largest number of admissions being in the months of July, August, September and October. The proportion of admissions to strength, about one-third, is somewhat higher than among the troops, but this is only to be expected when the inferior physical condition of the class of inmate is remembered. The interiors of most Indian jails are models of cleanliness and good sanitation ; but the boundaries of the hygienic oasis are abruptly limited by the jail walls, and immediately outside, the excavations that have yielded the material for their construction, brick pits, and ill-contrived drains, too often furnish breeding places in abundance for the malariacarrying Mosquito.
Moreover, the strict prohibition against the extra-mural employment of convict labour greatly ties the hands of the Superintendent in his efforts to improve the sanitary conditions of any spot beyond the four walls.
Having now considered, as far as space will allow, the conditions that influence the prevalence »or otherwise of Mosquitoes, it remains to be considered what can be done to diminish the pest. The malarial parasite has, it must be
CONDITIONS INFLUENCING PEEVALENCE 213 remembered, two distinct stages of parasitic life, each with its special host : Mosquitoes of the genus Anopheles during its period of sexual life and multiplication ; the human subject during its non-sexual stage : and it is obvious that the parasite may be attacked in either, or both of these stages.
The stage of the parasite that is passed within the human subject may be dismissed with a few words. As the end of all our efforts is the preservation of the host, all that can be done is to poison the parasite with quinine, or to isolate cases of malaria in such a manner that they cannot infect a relay of Mosquitoes. As regards the first method, a good deal is being done by the Indian authorities to popularise the use of quinine by distributing it through the agency of the Post office at cost price through the length and breadth of the land. At every Post office in India one can buy for a farthing five grains of excellent quinine, and though the amount so distributed, when stated as so much per head of the population, is insignificant, the amount sold is already much more considerable than most of us expected would be the case among a people so slow to avail themselves of new advantages as that of India. AYithin the present year a new effort in the same direction has been made by enfisting the agency of landowners to distribute the drug in the same semi-gratuitous fashion to their tenants ; and almost the last official duty it fell to the writer's lot to perform was to compile an indent for something like a hundred-weight of quinine for distribution in this way in a single district, a quantity which would have made his earlier administrative chiefs aghast with astonishment. Added to this, the invaluable services of Sir William King, F.K.S., late of our service, in establishing the cultivation of the cinchona plant in India, have revolutionised the price of the drug, and thereby conferred an incalculable boon not only on India but on all malariastricken humanity. The absolutely gratuitous distribution of quinine has been suggested, but personally I doubt if the cost to the consumer would be perceptibly less, for State benefits of this sort are woefully liable to be lost in
214 GNATS OR MOSQUITOES — CHAPTER VIII lubricating the smaller administrative channels through which they must needs pass after flowing beyond the ken of the large European distributory. In advanced countries, such as Italy, it is quite possible that the isolation of malarious patients might become practicable, especially as the large towns afford places free from the harmful species of Mosquitoes in which patients could be treated in the ordinary hospitals, without any special precautions for keeping out the insects ; but apart from the stupendous number of cases to be dealt with, such measures are out of the question in any malarious British dependency, and most emphatically so in India, where any attempt at enforcing isolation would infallibly result in political disturbance of the most serious character. To anyone who has passed a few months in the East such a statement will seem a superfluous truism, but so astounding and scathing are the comments on Indian administrative matters that are made by confident critics, as conversant with our social and climatic conditions as they are of those of the planet Mars, that it may not be out of place to record it. Turning now to the stage passed within the Mosquito, it is obvious that as we have no means of distinguishing infected from healthy insects, the solution of the problem lies either in the destruction of mosquitoes, or by avoiding being bitten by them. The consideration of the second class of precaution comes under the heading of personal prophylaxis, while the first must depend mainly on communal action. Measures designed to diminish the multiplication of Mosquitoes are of two classes, viz., those designed to check their increase by doing awa}' with the conditions that favour their breeding, and secondly, those that aim at the extermination of the race while leaving them to multiply at their own sweet will. Of the two, the first is, without question, the more efticient, but the practical sanitarian will not disdain to avail himself of the other class of expedient whenever it is practicable. It will be years before much can, however, be accompfished in the way of the really radical measures of the first class, and for the present we must content ourselves mainly with temporary expedients.
CONDITIONS INFLUENCING PREVALENCE 215 And here it may not be out of place to comment on the attitude of those who have been heaping cheap ridicule on those who have been working on this subject. The favourite expedient of this class of humorist is to impute to a man opinions he has never expressed and then to demonstrate how silly he must be to hold such doctrines. Applied to their own persons and profession they would be the first to resent the assumption that the shoemaker is, ex officio, incapable of using a last ; and yet they will have it that the fact of a man making a life-long study of sanitary problems renders him absolutely incapable of forming a rational judgment on the subject. The stock gibe of these good folks is to accuse Major Eonald Eoss, and others associated with him, with proposing to "exterminate Mosquitoes." Now I can assure them that though he labours under what they regard the incurable disability of being a scientific investigator, and a most distinguished one at that, he is, even outside his laboratory, no simpleton ; and no one but a fool would propose so impossible an undertaking, least of all a naturalist who has made a close study of the life-history of these insects. Between this and asserting that it is possible to diminish their numbers there is a very wide gap, though even on this score he has been singularly moderate, for the utmost that he has ever suggested as practicable is to check their free multiplication in certain special localities ; and of the practicability of this there can be no possible doubt.
While, however, none of us see any immediate prospect of being able to "stamp out malaria" or of wiping out the entire family of gnats, we find in that no reason for sitting with fatalistically folded hands, or of neglecting to utilise every possible method of keeping down their numbers, whether by doing away with every removable breeding place, or by directly destroying the insects in any stage of their existence. The fact is that there still remain numbers of people who regard disease as an inevitable infliction, which can only be dealt with by drugging, and to whom the conviction is strange that every disease must necessarily have a definite cause, which, sooner or later, will be dis-