290 NERVOUS FORCE. LECT. XIV. XV. 



tell you frankly, that until new facts are obtained with re- 

 gard to induced contraction, we cannot decide whether it 

 be due to a nervous induction, or be the effect of an 

 electric discharge occurring during contraction. 



If we could succeed by experiment in proving the truth of 

 the latter hypothesis, we should have made a grand step in 

 the analogies between muscular contraction and the elec- 

 tric function of fishes. 



Production of Nervous Force. In conclusion, let us say 

 a few words on the production of the nervous force. Al- 

 though it be true that we possess no knowledge of it ex- 

 cept in living animals, and consequently, want the appara- 

 tus to accumulate it and study its laws, out of the animal 

 itself, yet we should not abandon all physical analogies in 

 the investigations which we make relative to its mode of 

 production. 



Whenever a movement occurs, or the effect of force is 

 manifested, we are certain that some transformation of mat- 

 ter must have taken place. Wherever a force is exerted, a 

 chemical action precedes it. Caloric, electricity, and light, 

 furnish us, at every instant, with evidence of this truth. 

 But putting aside all analogies, let us examine the condi- 

 tions under which the development, of what we call nervous 

 force, takes place in animals. A man or animal, after a 

 long walk, having put his machine into motion, is fatigued, 

 and needs repose and nourishment. Although it be true 

 that facts are wanting to establish an intimate and really 

 scientific connexion between the effects of labour, repose, 

 and nourishment, on the one hand, and of the loss and 

 reparation of the nervous force on the other, yet we can- 

 not abstain from discussing these facts, complicated though 

 they be, on the principles of mechanics and general phy- 

 sics. 



Muscular exercise, of whatever kind, is constantly fol- 



