Page:Tropical Diseases.djvu/22

xvi prickly heat. But none of these states can with justice be regarded as disease.

This being so, it is natural to ask : In what way do tropical influences affect disease, as they undoubtedly do ; and why should it be that some diseases are peculiar to tropical climates, or are specially prevalent in such climates?

Speaking generally, the natives of tropical countries are not injuriously affected by the meteorological conditions of the climates they live in, any more than are the inhabitants of more temperate climates; their physiological activities are attuned by heredity and habit to the conditions they were born into. The European, it may be, on his first entering the tropics, and until his machinery has adjusted itself to the altered meteorological circumstances, is liable to slight physiological irregularities, and this more especially if he persist in the dietetic habits appropriate to his native land. A predisposition to certain diseases, and a tendency to degenerative changes, may be brought about in this way; but acute disease, with active tissue change, is not so caused. In the tropics, as in temperate climates, in the European and in the native alike, nearly all disease is of specific origin. It is in their specific causes that the difference between the diseases of temperate climates and those of tropical climates principally lies.

Modern science has clearly shown that nearly all diseases, directly or indirectly, are caused by germs. It must be confessed that although in many instances these germs have been discovered, in other instances they are yet to find ; nevertheless, their existence in the latter may be confidently postulated.

Germs are living organisms, and, like all living things, demand certain physical conditions for their well-being. One of these conditions is a certain temperature ; another is certain media; and a third is "certain opportunities.

In the majority of instances disease germs are true parasites, and therefore, to keep in existence as species, require to pass from host to host. If, during this passage from host to host, the temperature of the