entific form, and the one most fitted to aid investigations, the existing data bearing on this point.
What, then, to be precise, is the evil which threatens colonial populations, at first sight so little different from our own, and of which no external sign is apparent to reveal very profound transformations? The most powerful agent in producing degeneration, and to which doctors always give the first place, is the reduction of the formation of the blood in the organism. Is there really a retardation of this function, or an exaggerated destruction of the blood? I can not take the responsibility of deciding. Whatever it may be, emigrants are attacked with the same affection as in its phase of complete development among us is called anæmia. The more existence is tried by debilitating influences, the more intense becomes tropical anæmia.
But important as is its part, these debilitating influences do not consist of malaria alone, with its accompaniments of intermittent and other pernicious fevers, dysenteries, and liver-complaints; for even those whom the fever spares are not protected from tropical anæmia. The microscope has revealed to us many other morbid agents. Worms swarm in the tropics, particularly in the water, from which they pass to the body of man; and some of them abide in the blood. All such parasites may become destructive agents to the economy, which is subjected to a decline, the first manifestation of which is always impoverishment of the blood. With all our knowledge of the physiology of the blood, we are not yet able to explain, on the ground of merely theoretical data, the enormous loss of that liquid. We may admit that the preponderant part belongs to the destruction of the blood, while the absorption of air and oxygen is not increased.
A remarkable symptom, which is very well explained by an active destruction of the blood, is the strong predisposition to liver-disease. The liver is an organ the relation of which with the physiology of the blood is very intimate, and the troubles of which have the most influence upon the constitution of that liquid; and that is the organ which is the first object of the attacks, not only of malaria, but of the common diseases of acclimatization.
If I linger on these examples, it is to render more moving and more convincing the appeal which I make to doctors and naturalists to apply themselves to this sphere of research. Neither the French nor the English have as yet done anything important with reference to it. It is, then, a virgin field that falls to German science. It is also a subject of the highest importance; for we can not think of even an approximative solution of the problem till we have gained a precise idea of the modifications of the organism, and particularly of the special alterations of each organ, which are connected with the phenomena of acclimatization.
The popular masses, in their carelessness, seek the acquisition of gold. Show it to them, and they will plunge into perils without con-
