CHAPTER IV 



THE VITAL IMPETUS 



Two main conclusions emerge from the discussions of 

 the last three chapters : (i) that physiology encourages 

 no notions as to a " vital principle " or force, or form 

 of energy peculiar to the organism ; and (2) that 

 although physiological analysis resolves the meta- 

 bolism of the plant and animal body into physico- 

 chemical reactions, yet the direction taken by these 

 is not that taken by corresponding reactions occurring 

 in inorganic materials. From these two main con- 

 clusions we have, therefore, to construct a conception 

 of the organism which shall be other than that of a 

 physico-chemical mechanism. 



The ordinary person, unacquainted with the results 

 of physiological analysis, and knowing only the general 

 modes of functioning of the human organism, has, 

 probably, no doubt at all that it is " animated " by a 

 principle or agency which has no counterpart in the 

 inorganic world. This is the " natural " conclusion, 

 and the other one, that life is only an affair of physics 

 and chemistry, must appear altogether fanciful to any- 

 one who knows no more than that the heart propels the 

 blood, that the latter is " purified " in the lungs, that 

 the stomach and liver secrete substances which digest 

 the food, and so on. It is difhcult for the modern 

 student of biology, saturated with notions of bio- 

 chemical activities, gels and sols and colloids and 



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