The last remark is confirmed in a very remarkable manner by the numbers given in the accompanying table, which I borrow from M. Boudin. He gives a summary of the English official documents upon the annual mortality in the thousand at Sierra Leone from 1829 to 1836.
| DISEASES. | WHITES. | NEGROES. |
| Marsh fevers | 410·2 | 2·4 |
| Eruptive fevers | 0·0 | 6·9 |
| Diseases of the lungs | 4·9 | 6·3 |
| Diseases of the liver | 6·0 | 1·1 |
| Gastro-intestinal diseases | 41·3 | 5·3 |
| Diseases of the nervous system | 4·3 | 1·6 |
| Dropsy | 4·3 | 0·3 |
| Other diseases | 12·0 | 6·2 |
Sierra Leone is one of the most unhealthy stations for the White race, while for the Negro it is, on the contrary, one of the places where the rate of mortality is lowest. The relation which shows this difference is indeed most alarming (483·0 to 30·1). Yet the nosological table is the same for the two races, for although in this statement there are no eruptive fevers given for the English soldiers, we know very well that the White races are by no means exempt from them.
Other tables drawn up by M. Boudin, with the assistance of the same documents, bring into still stronger relief the fundamental fact now under consideration. In one of them we learn the comparative mortality of the Negro and the Black from marsh fevers in seventeen localities, taken from nearly all parts of the globe, from Gibraltar to Guiana, and from Jamaica to Ceylon. The number of deaths is always considerably greater for the Europeans, but they almost always rise or fall simultaneously, and in the same place, for the two races, when both are immigrants.
It is almost unnecessary to repeat the remark that all the great epidemics are common to all races, and that the yellow fever attacks indifferently the White, Yellow, or the Black race. The yellow fever is so far from being special in character, and is so subordinate to the action of the conditions of life, that Mexicans from colder regions are as liable to it as even Europeans; and in the islands of the Gulf of Mexico the creole Whites easily withstand those influences which are so fatal to immigrants.
IV. Eruptive maladies, and particularly small-pox, seem to have been unknown in America till they were brought by Europeans to that continent. On the other hand, the latter gave them some of the most serious forms of syphilis, which characterised the terrible epidemic of the fifteenth century. In this fatal exchange, the character of the two diseases was remarkably aggravated in passing from one race to the other, so that populations attacked by them for the first time would suffer much more than those who had communicated the disease. In America, whole populations have disappeared from eruptive fevers, sometimes with terrible rapidity. The celebrated tribe of the Mandans, when blockaded by the Sioux, and unable to escape this scourge, was entirely annihilated in a few days, with the exception of a few absent individuals. Catlin, to whom we are indebted for these details, and who obtained them from Whites protected by vaccination, adds that those who were attacked by small-pox, succumbed in two or three hours. On the other hand, we know what were the consequences in Europe of that infection, which, even at the present day, too often poisons the very sources of life.
Thus, a human race may be unacquainted with one, or several diseases, or with certain morbid forms, though at the same time but too apt to contract them. Once attacked, it may even develop this disease, which is new to it, in a more violent form than any hitherto known.
V. There are diseases which, though common to all human races, attack some in preference to others. The latter then enjoy, compared with the former, a relative immunity. This would necessarily result from what we have already seen. Let us add that these differences in the action of the same pathogenistic cause, are evident in cases of epidemics. When Guadaloupe was attacked by cholera in 1865 and 1866, the rate of mortality was 2·70 per cent for Chinese, 3·86 for Hindoos, 4·31 for Whites, 6·32 for Mulattoes, and 9·44 for Negroes. These figures are the more interesting from the fact that all these races were immigrants.
It seems sometimes, as if two causes of death maintained a kind of equilibrium and reciprocity between two races. I have already, when speaking of acclimatisation, pointed out the contrast which is presented by the Negro and the White from this point of view. Of all human races the White is most sensitive to marsh fevers, and the Black least so. On the other hand, the Negro race suffers more than any other from phthisis, while the White race may, in this respect, be almost classed with other groups, with the Malays for example.