A CCLIMA TIZA TION. 5 1 5 



entific form, and the one most fitted to aid investigations, the exist- 

 ing data bearing on this point. 



What, then, to be precise, is tlie evil which threatens colonial pop- 

 ulations, 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 develop- 

 ment among us is called anaemia. The more existence is tried by 

 debilitating influences, the more intense becomes tropical anaemia. 



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 

 anoemia. 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 knowl- 

 edge 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 in- 

 fluence 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 sub- 

 ject of the highest importance ; for we can not think of even an ap- 

 proximative 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- 



