THE VITAL FORCE. 61 



effect of a moderately high temperature in facilita- 

 ting chemical changes is well known, and its influence 

 upon life can be perfectly understood upon that 

 ground. Each tribe of living creatures seems to 

 have a range of temperature within which its vital 

 processes can be most perfectly carried on ; as we 

 see in the hybernation of some warm-blooded animals 

 during"winter ; and the similar state of inactivity to 

 which warmth reduces certain of the reptile class. 

 On vegetable life the influence of heat is so pre- 

 dominant, that Boussingault has made it the basis 

 of calculation, and states that the same annual plant, 

 in going through its complete development in dif- 

 ferent climates, receives on the whole the same 

 amount of solar light and heat, its time of growth 

 being shorter or longer, in strict proportion to their 

 greater or less amount. 



But further : in order to see fully the relation of 

 chemical action to the production of the vital state, it 

 is necessary to have recourse to the conception of a 

 resistance or limitation to it. A natural action, such 

 as the fall of a heavy body, as we have seen, may 

 bring about a condition opposite to itself; it is the law 



