222 PHYSIOLOGICAL DEVELOPMENT. 



cannot be rationally interpreted apart ; and throughout the 

 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 the 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. 



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

 considered from our present point of view as arising by 

 Evolution, must be carried on mainly by the study of the cor- 

 relative structures. Doubtless, by experimenting on the organ- 

 isms that are growing and moving around us, we 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 vary together — how 

 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 part dependent on his speed. 

 But though observations of this order 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. We have next to 

 no power of tracing up the genesis of a function considered 

 purely as a function — no opportunity of observing the 



