I. 



THE DURATION OF LIFE. 



With your permission, I will bring before you to-day some 

 thoughts upon the subject of the duration of life. I can scarcely 

 do better than begin with the simple but significant words of 

 Johannes Miiller : ' Organic bodies are perishable ; while life 

 maintains the appearance of immortality in the constant 

 succession of similar individuals, the individuals themselves 

 pass away.' 



Omitting, for the time being, any discussion as to the precise 

 accuracy of this statement, it is at any rate obvious that the life 

 of an individual has its natural limit, at least among those 

 animals and plants which are met with in every-day life. But 

 it is equally obvious that the limits are very differentl}^ placed 

 in the various species of animals and plants. These differences 

 are so manifest that they have given rise to popular sayings. 

 Thus Jacob Grimm mentions an old German saying, 'A wren 

 lives three years, a dog three times as long as a wren, a horse 

 three times as long as a dog, and a man three times as long as 

 a horse, that is eighty-one years. A donkey attains three times 

 the age of a man, a wild goose three times that of a donkey, 

 a crow three times that of a wild goose, a deer three times that 

 of a crow, and an oak three times the age of a deer.' 



If this be true a deer would live 6000 ^^ears, and an oak nearly 

 20,000 years. The saying is certainly not founded upon exact 

 observation, but it becomes true if looked upon as a general 

 statement that the duration of life is very different in ditierent 

 organisms. 



The question now arises as to the causes of these great 

 difterences. How is it that individuals are endowed with the 

 power of living long in such very various degrees ? 



