As in other infections, so likewise in malaria , badly nourished, not properly sheltered, overworked individuals are more frequently attacked than those living under better conditions.
An outbreak of malaria has not infrequently been referred, both by lay people and by physicians, to indigestion, excesses in Baccho, violent bodily efforts, psychic emotions, colds, etc. It is scarcely necessary to say that this is a false conception, though it is true that these influences may bring about a manifestation of a latent malaria. It is an interesting and important practical fact, to which we will recur again, that a person who suffered several months before from malaria may, as a result of these factors, display a relapse.
Slight traumas of the spleen, a douche over the region of the spleen, cold baths, mountain climbing, or the outbreak of another infection may act in the same way. Duchek has observed that in infected regions malaria not rarely follows pneumonia, typhoid fever, etc. All these cases are to be regarded as relapses. In the same category, too, I would place Griesinger's cases, in which persons who dwelt for a long time in malarial places manifested the disease for the first time after they had left these regions and gone to another healthy place. In some countries the eating of green fruit, especially melons or cucumbers, and sometimes even the drinking of milk, have been ascribed as the cause of the fever. This naturally could be true only in the previously mentioned sense.