AN ESSAY ON LONGEVITY. 8g 



effected. The American aloe reproduces and dies in 

 about five years in Mexico ; in England it elaborates 

 leaves for a hundred years before flowering. Again, 

 the axolotl reproduces in warm Mexico as a branch - 

 iferous amphibian; in colder climates its fertihty is 

 diminished, it becomes a salamandroid before repro- 

 ducing, thus lengthening life by delaying genesis. 

 It is rarely that we can point to such cases as these, 

 where the diminution of warmth affects sexual de- 

 velopment. Usually it will kill the animal or plant 

 experimented upon — as in the case of the mignonette 

 (a shrub in Barbary), and the palma Christi (a tree in 

 India), which both die annually in our severe climate ; 

 the longevity of the individual being in these cases 

 diminished rather than the fertility delayed. 



The two cases are interesting to compare with 

 man, who is believed to live longest in cold countries. 

 Like the American aloe, as is seen, when it is taken 

 to still colder climates than our own, or like the 

 mignonette in England, man ceases to gain in lon- 

 gevity when a certain limit of cold is attained. 

 Beyond the cold of temperate regions his longevity 

 is probably injuriously affected,^ as is that of the 

 palma and the mignonette in England, and that of 

 the aloe in regions farther north. The general action 

 of cold lies no doubt in the production of a sluggish- 

 ness of the chemico-vital changes, which, if carried 



' It is stated (Aitken's ' Medicine'), but not on statistical evidence, that 

 the longevity of the Icelanders is greatly reduced by catarrh. 



