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93. For many years the chief Vector in the Colony and New Territories was believed to be A. maculatus. The researches of Dr. Jackson have proved this to be incorrect. A. maculatus is a carrier but is of far less importance in the spread of malaria than A. minimus and A. jeyporiensis.
94. It appears that species of mosquitoes, like races of men, can under different conditions of climate and surroundings develop differences in habits and tastes for food. A. maculatus in Malaya readily takes human blood and is a very potent agent in the spread of malaria. In Hong Kong, where it is very prevalent, it seems to prefer animals to humans and its importance as a Vector of paludism is much less pronounced.
95. A. hyrcanus, the principal carrier in Shanghai, is here of little importance in the spread of disease. Its rate of infection under natural conditions is low and it has a preference for animal blood.
96. Investigations have shown that swamps, ponds, and other collections of water in the open plains away from the hills are more or less harmless and that the real danger lies within mosquito flight distance of the hills in the vicinity of which are to be found the breeding places of A. minimus, A. jeyporiensis, and A. maculatus. Why it is we do not know, but spring water which has not lost its sparkle does seem to have some attraction for these three species. As a rule, such water has a faint acid reaction due to dissolved carbonic acid gas. When it loses its CO2 and becomes flat, it ceases to attract.
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97. Though paddy swamps on the open plains are factors of little importance in the spread of malaria, the same cannot be said of the irrigated terraces which form the rice fields of the hilly country. These have been shown by the Malaria Bureau to be, under certain conditions, prolific breeding places for that powerful carrier A. jeyporiensis. The irrigation ditches leading to and from the rice fields harbour both A. jeyporiensis and A. minimus. Both of these species have a range of flight of at least half a mile.
98. Malaria not being a notifiable disease, few figures are available to measure the actual extent of incidence throughout the Colony and New Territories.
99. On the hospital returns and on the returns furnished by certain government departments, such as the Police, it is possible to base a guess as to whether the disease is on the increase or decrease generally, but that is all.
100. The cases admitted to Government Hospitals numbered 581, of which 21 or 3.6 per cent died. In the Chinese Hospitals, there were 1,341 admissions, of which 242 or 18 per cent died.