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PALUDRINE.

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Large scale observations were able to be made on the pro- tective prophylactic value of Paludrine amongst the troops situated in the New Territories who were on a daily dose of one (0.1 gramme) tablet.

Among the troops only 87 cases of malaria were notified by the Military Authorities and the majority of the cases arose either from omission to take Paludrine at all, taking it irregularly, or not taking it for a sufficient length of time. No cases of anemia following prolonged administration of Palu- drine were observed.

Experimental control of the Seventh Day Adventist School at Hang Hau by Paludrine alone was equally successful. Here a preliminary blood parasite rate was done at the beginning of the year among the 500 pupils, and again at the end of the season. Paludrine was taken voluntarily by half the pupils and a weekly prophylactic distribution was made in the villages in the neighbourhood of the school which was supervised by the school teaching staff. The pupils on protective Paludrine came from the North and had no local immunity. No case of malaria occurred amongst them, and there was no increase in the blood parasite rate. This, in a school where malaria was rampant before this method of control was introduced, was most satisfactory.

European and Chinese Police in the New Territories had equally good results on protective Paludrine.

FIELD WORK.

Rough training of streams, stone drainage, clearing, subsoil drainage, and oiling were the methods used. In addition a cheap experimental form of rough concrete training was carried out in the Deep Water Bay Valley which proved so successful last year that it has been used on the Stanley Peninsula. In addition to these larval control measures, the Chinese villages of Sai Wan, Pokfulam, Telegraph Bay and Ngau Chi Wan, on the outskirts of the control area, were residually sprayed with DDT. A determined effort to bring down the recurrent cost of the field work by more permanent methods was commenced by an attack on the sea coast breeding places of aedes Togoi, a great pest and a good carrier of filaria. Ilitherto it has been necessary to oil weekly the whole southern coast of the Island. This has been a difficult, and sometimes dangerous procedure in precipitous places,

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Funds for cement were made available by the Public Works Department and the Prison Department provided a daily labour force of 50 from Stanley Prison. Rock pools amounting to 9,500 were cemented in, and the whole of Stanley Peninsula has been permanently cleared of this species. This work is also being carried out by the Malaria Bureau at Keanedy Town, Pok- fulam, Aberdeen, Deep Water Bay and Shek O. It is hoped

in two years to rid permanently all the inhabited areas of the Island of this species; this will result in a big saving in oil, labour and supervision.

A further attempt for the purpose of increasing the efficiency of the work by cutting down the most expensive item, namely labour, is being made to find an insecticide which is efficient in uncleared water. Malariol has proved an efficient larvicide in cleared water and has the great advantage that using, as we do, unskilled labour, it is easy to apply and check by an unskilled staff, but it has the disadvantage (in local con- ditions) that the vegetation must be cleared first.

In conjunction with Imperial Chemical Industries, experiments with a new water miscible Gammexane were tried in certain uncleared streams in the New Territories. These streams which had previously been surveyed showed encouraging results with a 98% reduction of larvae after two applications.

Experiments are still going on to find a suitable dye so that the sprayer and supervising staff can check the work.

So far work has only been done in the dry season and it remains to be seen if this insecticide is equally good in heavy rain conditions.

Other work is proceeding with hormone weed killers to find a cheap method of keeping down local vegetation in streams. This is applied in the form of a spray.

NIGHT RESTING HABITS OF THE MOSQUITOES.

In order to determine the importance and value of Gammexane as a residual insecticide a series of observations on mosquito night flying habits were made during the period June to November. A Nissen hut, loaned by the Public Works Department, was sprayed on September 5th with Gammcxane midway throughout the observation period. The hut, not an ideal choice, was the only one available and was sited about a mile from Castle Peak Road, and about 50 feet above sea level. The nearest inhabitants of villages or huts were about half a