immunity from malarial fever on the part of the negro race is an acquired, not a congenital one, as we may learn by the frequent cases of sickness and death from this disease among the children of the negroes in Senegambia. But the same immunity is enjoyed by the natives of all malarious regions, so far as concerns their own home, and such other localities as are affected by malaria less severely than it; so that one might almost formulate a general rule that the predisposition to malarial sickness becomes weaker in proportion as the individual has been continuously exposed, from birth to maturity, to more or less severe malarial influences, without suffering from them to any considerable extent."—Hirsch, Geoqraphical and Historical Patholoqy, vol. i. pp. 243–4.
The passage last quoted furnishes an example of facts which may be accepted, but inferences which must be disputed. The sweeping generalization, that the "relative immunity from malarial fever on the part of the negro race is an acquired, not a congenital one," cannot be accepted as correct. Were it so, it would be as easy to rear European children in malarious countries as it is to rear the children of natives, and under equally insanitary conditions; whereas the fact is, that even under the best conditions procurable, it is difficult to rear European families in such countries as India, and practically impossible to do so in such countries as Senegambia. Moreover, characters which appear late in the ontogeny are not necessarily acquired. The superior immunity or much of it exhibited by adult negroes may be, and probably is, as truly congenital as are their permanent teeth or their beards. That some increase of resisting power may be acquired against malaria by continual residence in its presence is rendered certain by the fact, that natives of countries infested by it exhibit greater susceptibility when
