evidence to support my views on the subject, and I now append a very brief account of what I have found in reference to particular diseases, specific and otherwise.
Influenza.—Isolation for long periods from other races, as in the case of insular populations, causes influenza and similar epidemics to run a more severe and dangerous course; witness the cases of St. Kilda and the Society Islands. An epidemic takes place when the infecting visitors are afflicted with apparently only the slightest of colds, while less recent arrivals, if attacked, suffer far more lightly than do the older inhabitants, though more so than the visitors themselves. During my stay at Ascension Island I was told by a resident official that a cold introduced from a passing vessel runs through the island as a severe epidemic, necessitating rest in bed and active treatment for several days. This effect is still more virulent, leading even to fatal results, in the island of Tristan d'Acunha, where the isolation is much more complete, and the people are of British origin.
Now, sea-water is by no means the only method of isolation, and in earlier ages, situation, feuds, and scanty means of locomotion were efficient causes. When a tendency to a particular complaint becomes increased by long periods of isolation, so that heredity is able to accentuate any special proneness, one possible explanation of the origin of pathological racial idiosyncrasies is afforded.
Dengue.—African races incur this disease much less frequently than do others, and with them it takes a very mild form, being highly amenable to expectant treatment and simple care. On the other hand, the natives of India suffer in greater numbers and much more severely than do Europeans even, and show a much higher death-rate from it. Now, there are many African immigrants in India, and vice versa, yet this racial law still holds good among them, even after some generations.
Small-pox.—Both the negro and the Arab tribes in the Nile regions of Africa, and also the Aryan races of central Asia, have from time immemorial suffered cruelly from variola. Vaccination has lessened the value of comparative statistics on this point, but the mortality from the disease has been and is positively awful, complete depopulation sometimes resulting in particular valleys or islands.
Measles as an epidemic has caused terrible devastation among insular races, especially in warm climates, assuming a far more virulent type than that known to Europe, among people less capable of resisting a panic-creating disease.
Malaria.—Here occur the best instances of acclimatization of races. Ethiopians are affected less frequently than are other peoples, and with diminished severity. Blonde and blue-eyed Euro-