88 CONTEMPORARY SCIENCE 



internal causes even if all chance of infection and all acci- 

 dents are excluded. 



II 



These aseptic flies served as a means for testing an 

 idea concerning the duration of life which presented it- 

 self, namely, that old age and natural death are due either 

 to the gradual production in the body of a sufficient quan- 

 tity of harmful or toxic substances, or to the gradual de- 

 struction of substances in the body required to keep it in 

 youthful vigor, or to both. On this basis the natural 

 duration of life would be in reality the time required to 

 complete a chemical reaction or a series of chemical re- 

 actions, resulting in the production of toxic compounds in 

 a quantity sufficient to kill, or resulting in the destruction 

 of necessary compounds. Metchnikoff had called atten- 

 tion to the fact that toxic substances were formed in the 

 intestine under the influence of microorganisms. The in- 

 testine of aseptic flies is free from microorganisms, so 

 that the source for the shortening of life pointed out by 

 Metchnikoff need not be considered in this case. The 

 toxic substances formed might be substances formed in 

 one or several organs of the body during their normal ac- 

 tivity. Modern physical chemistry furnishes the means of 

 testing such an idea. The period of time required to 

 complete a chemical reaction diminishes rapidly when the 

 temperature is raised and increases rapidly when the tem- 

 perature is lowered. Experiments show that the time re- 

 quired for the completion of a chemical reaction is doubled 

 or trebled when the temperature is lowered by 10 centi- 

 grade. This influence of temperature upon the rate of 

 processes of nature seems to be typical for chemical re- 

 actions. If, therefore, the duration of life is the time 

 required for the completion of certain chemical reactions 

 in the body we might expect that the duration of life will 

 be doubled or trebled when we lower the temperature ten 



