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242 impressed with the belief that malaria is an actual or material poisonous substance. To Homer it was the arrows of Apollo in anger, to the mediæval folk-lore it was the mischief of elves and sprites; and, if scientific medicine does not now permit us to personify the malaria, it teaches us at least to materialize it. Although the fevers which malaria produces are quite unlike the fevers that are contagious or communicable, the present scientific guides of the profession are resolved to find a material virus or poison as the cause of them. The malarial poison was sought for, in the early days of chemistry, among the various gases of the marsh, but the chemical search proved fruitless. "When the microscope came in, the miasm was diligently looked for in the soil of malarious localities and in the vapors overhanging them. From 1849 to the present year, some twenty different vegetable organisms or their spores, of very various degrees of complexity, have been described each in its turn as the malarious miasm and as the specific cause of remittent and intermittent fevers; and the quest for a material substance assumed to be the cause of malarial fever is regarded with much favor in the best scientific circles. Meanwhile a body of opinion, which takes due account of all the manifold associated circumstances of malaria throughout the world, has been forming, and yearly growing in volume, that there is no malarious miasm at all; that "malaria," indeed, is a profound disorganization of the nervous mechanism that presides over the temperature of the body; and that this upsetting of the heat-regulating center is likely to happen when the body has been exposed during the day to extreme solar heat and to fatigue, and exposed at sundown and in the night to the tropical or sub-tropical chill, which will be severe in proportion to the rapid cooling of the ground and the amount of vapor condensed in the lowest stratum of the air. There is no more beautiful mechanism in nature than that which keeps man's internal heat always about 98° day and night, summer and winter, in the Arctic regions or in the tropics; but even that most wonderful of all self-adapting pieces of mechanism, if it be taxed too much, as by extremes of day and night temperature, will get out of gear; and a fever, still retaining something of the diurnal periodicity, will be the result. No one can read the powerful criticism of Surgeon-Major Oldham, of the Indian Medical Service, without discovering this rational explanation of malaria to have the best of the facts and the best of the logic on its side.

The decision of this point of theory one way or another has the most momentous issues, not so much for the treatment of malarious fever as for its prevention. It is, in short, a question, on the one hand, of common prudence in warm countries, more often moist than arid, and more often level than mountainous, against exposure of the body to the direct action of the sun's rays and to the nightly chill