The climate is healthy and bracing, except in the lower valleys along the river banks and in the marsh land, where malarial fever is prevalent.
Districts which had been notoriously deadly to Europeans were rendered comparatively healthy after the discovery, in 1899, of the species of mosquito which propagates malarial fever, and the measures thereafter taken for its destruction and the filling up of swamps.
The malarial cachexia that follows definite attacks of ague consists in a state of ill-defined suffering, associated with a sallow skin, enlarged spleen and liver, and sometimes.
It has, however, an evil name for malarial fever.
The valleys and coast belt, though practically free from malarial fever, are hot and humid, and fires in dwelling houses are seldom required even in the coolest months; the lower plateaus are cool and the air dry; the uplands are bracing and often very cold, with snow on the ground in winter.
The labours of Golgi, Marchiafava, Celli and others established the nature of the parasite and its behaviour in the blood; they proved the fact, guessed by Rasori so far back as 1846, that the periodical febrile paroxysm corresponds with the development of the organisms; and they showed that the different forms of malarial fever have their distinct parasites, and consequently fall into distinct groups,.
The Chinese immigrants suffer chiefly from fever of a malarial type, from beri-beri, a species of tropical dropsy, and from dysentery.
Horsesickness, a kind of malarial fever, which takes an epidemic form in very wet seasons, causes considerable loss.
Among the mosquitoes, which are extraordinarily numerous in some of the hot lowland districts, are the species credited with the spread of malarial and yellow fevers.
Following up this line of investigation, Major Ronald Ross in 1895 found that if a mosquito sucked blood containing the parasites they soon began to throw out flagellae, which broke away and became free; and in 1897 he discovered peculiar pigmented cells, which afterwards turned out to be the parasites of aestivo-autumnal malaria in an early stage of development, within the stomachwall of mosquitoes which had been fed on malarial blood.