AN ESSAY ON LONGEVITY. 129 



21. Abnormal Longevity in Man. 



A few words remain to be said on this subject 

 from a general point of view. It has been often 

 treated of under the head of Longevity by able writers 

 and curious speculators. An article in the 'Quar- 

 terly Review' of January, 1868, and one in the 



marry sooner and live longer than the unhealthy offspring, so that a 

 very minimum of injury is done to the race by warding off the selective 

 destructiveness of disease : inferiority must produce its legitimate results 

 in spite of man's interference. Moreover, the mixing of stocks, virith 

 a tendency only to certain diseases, may be a source of strength, im- 

 plying as it does mixture of varied constitutions. The tendency to 

 particular diseases under given conditions is not a proof that under all 

 conditions which may arise there will be that tendency. If the con- 

 ditions are changed, as they are rapidly changed in the progress of 

 civilization, what was weakness may become strength, a constitutional 

 tendency to one kind of disease being associated with immunity from 

 other kinds. Little is known on this matter ; but compare the ravages 

 of small-pox among Africans, of syphilis among Europeans, and the 

 immunity of the Maoris from any severity under these diseases (' Fenton's 

 Report,' loc. cil.). The effect of sanatory action in preventing the natural 

 elimination of ' fermentable ' matters from the blood (Paget) of gene- 

 rations is a curious subject for speculation. Zymotic diseases, if allowed 

 to run their course unchecked in a community, kill off those individuals 

 most imbued with this supposed fermentable matter, or remove it from 

 those who recover from their attacks. If zymotic diseases are kept off, 

 will not the ' fermentable matters ' increase from generation to genera- 

 tion? It seems as though such elimination as vaccination should be 

 adopted, together with sanatory measures, or we may accumulate a 

 nidus in the veins of posterity. Possibly, if exempt for great length of 

 time from a disease, a species may become no longer subject to it, just 

 as two closely allied species of animal, e. g. the sheep and ox, are not 

 subject to the same diseases, though presumably descended from a not 

 remote common ancestor. • 



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