OF FUNCTION; OR, HOW WE ACT. 3 



No science lias made real progress till it has passed 

 out of this state. So long as no certain principles 

 or necessary laws have been discovered in any 

 branch of knowledge, we cannot tell what we may 

 believe, and, at the best, its doctrines form a mass 

 of truth and error inextricably mixed. 



If, therefore, any relations in the vital processes 

 coulcWbe ascertained, which must in the nature of 

 things be true, like the propositions of geometry, 

 or if any physiological laws could be found, based 

 on a sufficiently wide induction to give them 

 authority as standards, like the laws of gravitation 

 in astronomy, or of definite proportions in chemistry, 

 this would be a great aid both to the comprehension 

 and to the advance of the science. And though we 

 do not intend here to enter on any such inquiry 

 we may try whether a clearer light cannot be thrown 

 upon some of the points on which the main interest 

 of physiology centres. 



Too much must not be attempted at once. So, 

 dismissing for the present all other subjects con- 

 nected with the living body, we concentrate our 

 attention on the question, Whence comes its active 



12 



