n6 AN INTRODUCTION TO SCIENCE 



the nerve-cell or the nerve-fibre should in any way select or 

 elaborate the messages which it transmits, still less has it 

 any antecedent or prescriptive right to decide to which of 

 all the contractile cells its messages shall be delivered. 

 Shall the type-writing machine decide which letter it will 

 write, or whether it shall print it in small type or capitals 

 when the key marked m or n is pressed? In its original 

 form the nervous system is as mechanical in its action as a 

 type-writing machine. But in the complex state of organiza- 

 tion to which it attains in the higher animals, how far it 

 seems to have advanced upon a mere arrangement of levers 

 pressed down by forces from the outer world ! And in our- 

 selves, when we study its working by introspection, when we 

 feel it selecting, suppressing, exaggerating, and apparently 

 originating the messages which it transmits, how far it seems 

 to be from an automatic machine played upon by our 

 environment. Herein lies the crux of this great problem. 

 The animal is a mechanism. The animal has a will. The 

 physiologist who looks upon the nervous system as a means 

 of communication between sense-organs and muscles is 

 content to study its connections. The psychologist who 

 regards it as the body-tissue in which the impulses im- 

 pressed upon the body from the outer world are " worked- 

 up," seeks for some protoplasmic substance, which, owing 

 to its molecular instability and the chemical changes which 

 consequently occur, is capable of manufacturing impulses, 

 or at any rate of storing and profoundly modifying those 

 which pass through it. 



The controversy between those who hold the mechanical 

 view and those who incline towards the automatic theory, 

 as physiologists would term it meaning thereby the con- 

 ception of the nervous system as an originator of nerve- 

 currents is as old as the science of physiology ; not that 

 we wish to imply that the science properly so-called has as 

 yet reached "years of discretion." It is useless to ask 

 when it first assumed the exactitude of a science. We 



