of the high level of immunity among the native New Territories population together with the progressive lowering of the trans- mission rate of this disease since the Japanese occupation,
122. In regard to the former, morning catches of mosquitoes were made daily in selected villages in the New Territories. Some were in villages in flat areas where A. hyrcanus prevails and some in hillfoot villages where A. jeyporiensis and A. minimus predominate. Altogether 9,445 anophelines were dissected but none were found to be infected. In the morning catches, after very careful search, it became increasingly clear that A. minimus and A. jeyporiensis were only to be found resting in houses where cattle or pigs were also housed, whereas any number of well fed C. fatigans were obtained without difficulty in the dwellings containing no cattle.
123. Confirmation of this habit of the local species largely resting where cattle were housed was confirmed in the results of precipitin tests on blood taken from the mosquitoes. In 322 tests carried out, 198 were positive for cattle, 17 for pig, 13 for dog, and only 21 for human blood, This means that propor- tionately only about some 600 of the 9,445 dissected mosquitoes are likely to contain human blood. Further confirmation of this point is available from observation of the night biting habits of the local anophelines. Over a period of 20 days the number of anophelines biting two human bait in a nissen hut in the New Territories was observed from dusk to dawn. There were no cattle in the hut, and in this period, 757 anopheline mosquitoes were counted biting. A subsequent morning search of the building revealed only two anophelines. However, it is proposed to spray two entire villages where catching has been carried out for a year, and to observe the effect on the morning catches of mosquitoes, and the blood parasite rate of the inhabitants.
124. In regard to the natural immunity of the New Terri- tories population to malaria, this is undoubtedly high. It was found that new cases now largely occur among incoming Northerners and other non-immunes.
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125. Recent examinations in the New Territories villages show a very low blood parasite rate, an average of 4.33% in October and 1.51% in March. This immunity does not appear to be obtained at the expense of a high infantile mortality rate.
Tai Lam Chung
126. At Tai Lam Chung Dam, malaria control work com- menced six months before the coolie lines were occupied. The value of this precaution is evidenced by the fact that no cases of malaria have so far occurred amongst the present labour force of 240.
Tuberculosis Control
127. Some idea of the magnitude of Hong Kong's tuber- culosis problem may be obtained from the fact that tuberculin testing indicates that almost 95% of the population above the age of 14 years has already been infected by the disease. The large numbers of unemployed and the consequent low standard of living, added to overcrowding almost without parallel, gives rise to a set of circumstances in which one might expect to find the disease in epidemic form. More than one-third of the deaths from tuberculosis occurred in children under the age of 5 years, mainly from progressive primary tuberculosis and tuberculous meningitis. With these facts in mind a B.C.G. programme was commenced with the ultimate object of attempting to offer vaccination to all new born children. In adults morbidity was highest in the 30 - 35 age group, and mortality greatest in middle and later life. The high racial resistance of the local population prevents the disease from exacting a higher toll of life but produces at the same time a type of disease which gives rise to a large proportion of infectious ambulant cases, which, in view of the type of housing and the degree of overcrowding, pass on the disease to their numerous close contacts. In these circum- stances a realistic control programme is virtually impossible. Satisfactory home isolation is impracticable and hospital isolation is impossible because of the shortage of hospital beds. While the tuberculosis services may, with their present resources, do much to assist the individual sufferer, the present scale of operations is unlikely to affect the problem as a whole,
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