AN ESSAY ON LONGEVITY. 87 



which are fattened for eating, and are beheved to be 

 short-lived in consequence. It is clearly the case in 

 pets, such as small dogs, whose life is shortened by 

 luxury. Hounds are the longest lived amongst dogSi 

 On the other hand, there p.re cases in which man, 

 by his care in avoiding expenditure, has lengthened 

 his own and other animals' tenure of life ; and it 

 appears, from the little that is known, that experi- 

 mental evidence does support the proposition, that 

 longevity is lengthened by diminution of personal 

 expenditure. 



13. Summary. 



Hence, in spite of the great complication of the 

 case, we may conclude, on both deductive and 

 inductive grounds, that the high or low potential lon- 

 gevity of different species, as a general law, is neces- 

 sitated by those conditions of life which necessitate 

 high or low individual development, as the case may 

 be, whether of mere bulk, or complexity, or both ; 

 that it is directly subject to those conditions which 

 cause personal expenditure to fluctuate, or which 

 affect generative expenditure, being high when these 

 are low, and low when these are high ; that these 

 relations interacting and contending variously ac- 

 cording to the special case, determine the potential 

 longevity of the various species of lower animals. 



From the intricacy of these relations we may con- 

 clude that potential longevity is a very delicately 



