A chart drawn to show the rainfall, the ease-returns, and the case-rate (i.e., the number of cases per cent, of population) every year, and also these data computed for the 12-monthly periods from June to May revealed no direct correlation in them ; indeed, between the incidence and the rainfall there was a tendency to inverse correlation (Chart 3). There was, however, no doubt about the inverse relationship if the data were compiled for the period January to May of the year, and the inversity was also evident in the June to December period (Charts 4 and 5). These findings then indicate that the pathophors here are stream-breeders, and this conclusion is supported by the fact that the writer had much difficulty in capturing any stream-breeders after the fall of several " MALARIA ON AMBOOTIA ESTATE very heavy chota-monsoon" showers just NEAR AND THE SUCCESS previous to his visit, and that " " swamp- OF SOME ANTT-MALARTAL OPERA-. breeders were absent. TTONS. v The circumstance of the inversity, within of case-rate to By C. STRICKLAND, m.a., B.ch. (Cantab.), any period, rainfall does not give much scope for the Medical School predicting severity Professor of Entomology, of Tropical of the season; but a Medicine, Calcutta. epidemic good means of prediction was discovered by charting yearly rainfalls case-rates for The of hill-stations is an import- against the period malariology to ant for visitors do not go to them to January May following, during which the subject, well their abed with fever. Any contri- epidemic becomes established. It then spend holiday that the the bution, therefore, to our knowledge of the sub- appeared greater monsoon rain- fall the less the case-rate in ject may be helpful. any year, the season next The observations now recorded were made epidemic year. Marjoribanks to malaria on in May 1923 during a visit to Ambootia Tea (1914), referring Salsette about 3.000 Island, has averred the same fact in his Estate. Kurseong, feet above " sea-level in the Eastern Himalayan foot- statement that a dry year followed by an causes an increase of hills. They indicate the salient factors which ordinary year malaria- incidence." and Gill determine malaria incidence on the estate; Christophers (1911) have the and their analysis throws into relief the (1922) recognised general import- ance able to effect of the anti-malarial operations which of being predict malaria epi- in forth the had been initiated with uncommon enter- demics, setting factors conducing to them in the prise bv the Manager. Mr. A. O Brien-Webb, Punjab. - the fact on at the instigation of the Visiting Medical Officer, Incidentally that Ambootia Estate a monsoon is Dr. Kingsley-Ward. The nature of the opera- heavy year followed by a tions was mainly the drainage of swamps and light epidemic year, proves that on these training of streams. slopes seepage of subsoil-water for months after the monsoon does not occur In the course of the work the first point to any one considered was whether the rainfall had extent. If it did, would feel sure that anything to do with the malaria-rate. there would be a rich legacy of dangerous Generally speaking when a malaria-rate spring-water breeders such as A. maculcitus corresponds with a moderate rainfall, one causing much trouble long after the rains is not the case. would incriminate swamp-breeding ano- cease, but this Probably the micaceous so phelines; while if such data have an inverse decomposed granite soil here is that water flows relationship stream-breeders might be sus- porous away through, al- most as as it. pected; the reason being that heavy rains readily over, scour out the breeding places and so diminish The relationship between rainfall and the sources of malarial infection. This has malaria was further analysed in Chart 7, been emphasised by Perry (1914) with where the monthly records from 1917 to 1923 reference to the Jeypore hill-tracts. are given. Apart from any question of rain- The estate records which were necessary fall-malaria correlation it must be observed to decide the point had been in charge of the in this chart, that subsequently to March. Medical Officer of the estate and the conclu- 1922, when Mr. Webb started his anti- sions submitted are drawn from the analysis malarial operations (as noted above) the of those from 1917 to the present time. improvement of health was immediate and 120 THE INDIAN MEDICAL GAZETTE. [March, 1924. sustained. The reason for this was probably Chart 7 giving also the temperature records, the fact that the troublesome mosquitoes, ?leads to the following conclusions:? being stream-breeders, had been subjected (a) In the pre-monsoon period, from by means of the more than November to February inclusive, the malaria operations " to the force of the chotamon- case-rate of the succeeding month goes up naturally" soon showers. independently of both the monthly temper- The monthly data have been condensed in ature and the rainfall. Probably the slight Chart 6 into two periods, first for 1918-21 and rise in case-rate is here due to recurrences then the years 1922-23 during which anti- induced by cold and exposure.

5 rJ.F.MAM.J.JLA.S.QK.c'.UEMAM.iJ.A.S.aK.i'J.EMAKJ.j.A.5aHO'.3.F.M.AJuj.A.illS.ff.0.F.lii>HJ.J.A.iaH.o:'JF.KAi(.J.J.A.5-O.Ml ^ I I i 1 I I

Chart I. Cases ??

Chart 2.

Case rate ?- ?! L I ,, in MONTHS Jah-MAY ChartHART 3.<3. yearly.

Rainfall 20 IN UMCF'CRKDK YfcARLY. | 500 300 Cases in same period

Chart 4.

Chart 5.

Chart 6. CAitHRTE 1 Rainfall.

ChartChjvrt 7.

malarial operations have been in progress, but (b) After February until May the same in this chart rainfall has been apposed to the data are very closely correlated; malaria incidence of the subsequent month (c) which proves that the rising- rainfall for the reason that the development of the with its tendency to depress the case-rate mosquito and its malaria parasite and its is counterbalanced by some other factor, and incubation in man takes a month or more to this is probably, at this time of year, the complete. A study of the chart and also of rising temperature. Chart 7 which gives the same data on a (d) After the monsoon breaks, the great larger scale (for the early months only),? increase of rain in June and July, is responsible March, 1924.] NOTEo^N ANTI-PLAGUE VACCINE: STOCKER & GRAHAM. 121

of malaria in and Summary. for a rapid decline July August; An analysis of the malaria-rate with factors on (e) which proves that the May brood of possible contributory Ambootia mosquitoes begins to die out by July, and Tea Estate near Kurseong, Eastern Hima- cause leads to the that in general mosquitoes do not layan foot-hills, conclusion that trouble by living long. the amount of rainfall bears an inverse (f) When the rains abate rapidly the relation to the malaria-rate at all times of the malaria-rate falls less rapidly. year. Probably the most important factor are the (g) When anti-malarial operations in the production of annual epidemic in in is a being carried on, as seen the second part the spring months rising temperature. of Chart 6, the lighter increase of rain in The inverse relationship of the rainfall May is responsible for a striking fall of case- indicates stream-breeders as pathophors, and A. willmori found rate in June or a month before normal. A. maculatus and being every- (h) The effect of anti-malarial operations where, should 'be incriminated with causing the has been to cause a general decrease of trouble. malaria incidence. The inversity of the rainfall to the malaria- rate a means of the In confirmation of the conclusion that the also provides predicting But a anti-malarial operations on Ambootia Estate severity of the latter. better method was that the of have been effective in reducing malaria, the found by showing severity the monsoon is inverse to that of the following facts may be cited:? epidemic in the next Division A in 1921 had no operations and year. The of subsoil water for months 122 cases: in 1922 slight operations and 133 seepage after the monsoon is not a factor of cases. Whereas in habitats for the Division B in 1921 had no operations and importance affording nor is the continued existence of 56 cases: in 1922 no operations and 112 cases. pathophors, brood of A Further, Division C in 1921 had no opera- any mosquitoes. breeding ground of A. maculatus and A. willmori at a distance tions and 185 cases: in 1922 most intensive of about 1,300 yards and 500 yards vertically operations and 92 cases. below is of no economic importance.* While Division D in 1921 had no operations Anti-malarial started at the and 283 cases: and in 1922 after operations operations of Dr. the 138 cases. instigation Kingsley-Ward by Mr. have been The most immediate factor in Manager, O'Brien-Webb, very important that the of the situation must be the mosquito fauna and successful. They prove drainage of streams in which A. its habitat. That the mosquitoes causing the swamps and training maculatus and A. willmori breed are effective trouble are stream-breeders was the conclu- anti-malarial measures, sion come to from the preliminary analysis though complete success from their is not to be above, and those found on the estate employment given Not have reduced the were A. wilhnori, A. maculatus, and A. aitkeni: expected. only they but this has fallen a the first two, of course, being very dangerous. malaria-rate, rapidly the normal fall would take Other species taken were lindesaii, barbirostris full month before of the Mr. O'Brien-Webb should be and vagus, while outside estate in stony place. congra- pools of the bed of the Balasun river A. willviori tulated on his good work. and A macnlatus were caught in very large References. numbers. Christophers, S. R-, 1911. Epidemic Malaria of the The Balasun flows in a valley 1,500 feet Punjab with a note on a Method of Predicting Epidemic No. 1911. below the estate about three-quarters of a Years. Paludism, 2, Jan. Gill, C. A., 1922. The Prediction of Malaria Epide- mile off as the crow flies and whether the mics. Iiid. J I. Med. Res., Vol. 10. valley was not a very great danger or not Marjoribanks, 1914. Malaria on Salsette Island. I)td. was a matter for serious consideration. Jl. Vol. 2. Med, Res., _ Probably it is not, however, for one section Perry, 1914. Endemic Malaria of the Jeypore Hill Tracts. Ind. Jl. Med. Res., Vol. 2. of Division A of the estate with a spleen- index of 0.00 per cent, is situated on a knoll directly above the river, nearer in fact than any other division. The main object of the observations was to localise the sources of danger on the estate and those made, it is hoped, will enable the Manager, Mr. O'Brien-Webb, to complete the work which has already borne good fruit. To him, as also to Drs. Kingsley-Ward and Winckler the writer owes thanks for the

received and he is also indebted to * help Watson in Malaya has found that breeding places ol Lt.-Col. McCombie Young, i.m.s., for his useful the strong flier A. urnbrosus at a distance greater than a criticism of the draft report. quarter of a mile are of no economic importance.