88 'EX VIS IB US VIVIMUS. 



balanced quantity, and that very slight causes may 

 produce great fluctuations in it, and be almost im- 

 possible to trace ; the magnitude of the result being 

 far larger than in proportion to the magnitude of the 

 initial cause, as is so often found to happen in 

 Biological Science. 



The Longevity of Man. 



14. Preliminary. 



In this part of the essay, our object is to apply 

 the conclusions we have obtained from the study of 

 organisms generally to the case of man, and es- 

 pecially to observe how far his obedience to the 

 general law is affected by, or dependent on, the 

 different phases of civilization which he exhibits. 



Man presents the most marked contrasts with 

 animals generally in many of the chief conditions of 

 existence affecting longevity. Civilized man lives in 

 societies, one of the most essential bonds of union in 

 which is the maintenance, to a greater or less extent, 

 by the community of the feeble. The security which 

 the healthy and vigorous man hopes for himself, when 

 grown old and feeble, he naturally extends to others, 

 and thus the aged are fed and protected as the result 

 of a specific habit or characteristic among men (the 

 most barbarous excepted). 



Further, the intellect of man renders him utterly 

 unlike animals in much that relates to age ; for 



