CIRCUMSTANCES FAVOURING THE CLINICAL
MANIFESTATION OF MALARIAL INVASION
As a rule, a successful malarial infection declares itself within a week or ten days. As with other infections, certain individuals resist the pathogenic influences of the malaria parasite for a longer period. A very few appear to be permanently immune. Everything tending to cause physiological depression favours susceptibility and acute manifestations.
Influence of meteorological conditions on relapse.—— A malarial subject while in the mild climate of the tropics may keep in fair health; but when, as is so often the case with sailors and others returning to Europe, he is plunged into the stormy winter of the North, is exposed to cold, and has long watches and fatiguing work, very probably latent malaria will become active and ague follow. This is a common experience with malarials from the tropics. It is almost the rule with people coming from the West Coast of Africa. Stanley remarks that so long as he and his companions were ascending the Congo, the wind being with them and therefore not much felt, they did not have fever ; but that on descending the stream, a strong breeze blowing in their faces and chilling them, they constantly had attacks. The physiological depression and disturbances caused by the cold wind paralysed the self -protecting power of the body, and permitted the hitherto latent parasite to get the upper hand. And so it is found, in the highly malarial districts of tropical Africa, that houses perched on elevated and windy situations are not so healthy as those on lower and, therefore, less exposed and more sheltered ground. This must not be interpreted as showing that wind causes or carries malaria. The wind merely acts as a cause of physiological strain, of chills; it acts just in the same way as fatigue, hunger, a wetting, disease, fear, excesses, or depressing emotions are found to do.
Sex, age, occupation—— Sex per se seems to have no particular influence as regards liability to or severity of malarial attacks. Neither has occupation;
