222 rHYSIOLOGICAL DEVELOPMENT. 



cannot be rationally interpreted apart ; and tliroughout tlie 

 foregoing pages this truth has been made abundantly mani- 

 fest. Here we are obliged to recognize the inter-dependence 

 still more distinctly ; for the phenomena of function cannot 

 even be conceived without direct and perpetual consciousness 

 of the phenomena of structure. Though the subject-matter 

 of Physiology is as broadly distinguished from tlie subject- 

 matter of Morphology as motion is from matter; yet, just 

 as the laws of motion cannot be known apart from some 

 matter moved, so there can be no knowledge of function 

 without a knowledge of some structure as performing func- 

 tion. 



Mucli more than this is obvious. The study of functions, 

 considered from our present point of view as arising by 

 Involution, must be carried on m-.dnUj by the stud}^ of the cor- 

 relative structures. Doubtless, by experimenting on the organ- 

 isms that are growing and moving around us, v/e may 

 ascertain the connexions existing among certain of their 

 actions, while we have little or no knowledge of the special 

 parts concerned in those actions. In a living animal that 

 can be conveniently kept under observation, we may learn 

 the way in which conspicuous functions var}^ together — hov/ 

 the rate of a man's pulse increases with the amount of 

 muscular exertion he is undergoing ; or how a horse's 

 rapidity of breathing is in pi^rt dependent on his speed. 

 But though observations of this oider are indispensable — 

 though by accumulation and comparison of such obser- 

 vations we learn which parts perform which functions— 

 though such observations, prosecuted so as to disclose 

 the actions of all parts under all circumstances, constitute, 

 when properly generalized and co-ordinated, what is com- 

 monly understood as Physiology ; yet such observations 

 help us but a little way towards learning how functions 

 came to be established and specialized. AVe have next to 

 no power of tracing up the genesis of a function considered 

 purely as a function — no opportunity of observing the 



