AN ESSA Y ON LONGEVITY. 



far towards enabling us so to do. From the time of 

 Aristotle onwards, observers and philosophers have 

 accumulated facts and multiplied speculation on the 

 causes of longevity : the field is a well-trodden one, 

 and for many years to come any increased knowledge 

 of it must be looked for rather from the examination 

 of long-acquired facts and their re-arrangement, than 

 from new or unexpected observations ^ by individual 

 workers. 



2. Writers on Longevity ^ and general Sources of 

 Information. 



In consequence of the general nature of the en- 

 quiry proposed in this essay, we have little in 

 common with those who in former ages have en- 

 larged upon the possible means of prolonging human 

 life ; nor are we concerned specially with those 

 questions as to the possible and extreme periods 

 of man's tenure of existence, which to-day occupy 

 the attention of many literary men of an antiquarian 

 or curious turn of mind. In the writings of these 

 men we cannot expect to find more than one limited 

 class of facts bearing on comparative longevity ; and 

 in too many cases the facts so called are not sup- 

 ported by scientific evidence. In a recent article in 



' It will be seen below how vast an amount of enquiry has yet to be 

 made, as to length of life in animals and men. No single individual can 

 do much in this matter in less than a lifetime. 



B 2 



