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30 occurs in the trail of man. It is quite likely that the artificial conditions of sewage and garbage set up by man on the sea-coast are responsible for the prevalence of this parasite, and the weakly receptivity of the too-numerous sand-hoppers.

It is probable enough that, from time to time, under the influence of certain changes of climate and associated fauna and flora—due to meteoric or geologic movements—parasitic disease has for a time ravaged this or that species newly exposed to it; but the final result is one or other of the alternatives, extinction or adjustment, death or toleration. The disease does not establish itself as a scourge against which the diseased organism incessantly contends. It either obliterates its victim or settles down with it into relations of reciprocal toleration.

Man does not admit this alternative either, for himself or for the domesticated and cultivated organisms which he protects. He 'treats' disease, he staves off 'the adjustment by death,' and thus accumulates vast populations of unadjusted human beings, animals and plants, which from time to time are ravaged by disease—producing uncertainty and dismay in human society. Within the past few years the knowledge of the causes of disease has become so far advanced that it is a matter of practical certainty that, by the unstinted application of known methods of investigation and consequent controlling action, all epidemic disease could be abolished within a period so short as fifty years. It is merely a question of the employment of the means at our command. Where there is one man of first-rate intelligence employed in detecting the disease-producing parasites, their special conditions of