24 EX VIRIBUS VIVIMUS. 



worth while speculating as to what may best serve 

 this purpose, since in no animal or plant are we in a 

 position to make use of any decision on the matter, 

 and in the case of man it will be seen that it is not" 

 much wanted. The day may, however, come when 

 sufficient observations will have been made on lower 

 organisms to render such a fixed point of comparison 

 useful. 



Potential longevity differs then in different species 

 (as a glance at the statements as to longevity below 

 will fully prove), and agrees within certain limits in 

 individuals of the same species. Why is this .'' It 

 is no doubt because the particular structure and 

 habits of each species in some way require or entail 

 the particular limit or lease of life. But how is this 

 effected .■" Does the life of a given species receive 

 its limit simply through the operation of the par- 

 ticular or specific external agencies (to which the 

 species is born and' specially constructed to meet) 

 on each individual born } Undoubtedly this is so 

 to a large extent. For man may take an animal 

 lower than himself in the scale of life, or a plant, 

 and by his care and attention, by removing the 

 agencies to which the creature is born, and care- 

 fully substituting others, may cause it to live much 

 longer than it could possibly do if left to its natural 

 conditions. Thus man may take a bird, and by 

 providing it with food, and protecting it from com- 

 petition with its fellows, from accidents and enemies, 



