262 NERVOUS FORCE. LECT. XIV. XV. 



seen, that in them the property which they have of giving 

 the discharge is under the immediate dependence of the 

 functions of the nervous system, as well, also, as is the 

 faculty which the muscles have of contracting.* 



A crystal of tourmaline, when heated, develops electri- 

 city, and from this fact we assume, that between caloric 

 and electricity there exists a more or less intimate relation. 

 The phenomena which we have observed in electrical 

 fishes, prove that a link of the same nature unites the 

 nervous force and electricity. Electricity is not the nervous 

 force, nor is caloric electricity. The latter is derived from 

 caloric in consequence of the form of the integral mole- 

 cules of the tourmaline ; the nervous force is transformed 

 into electricity under the influence of the peculiar structure 

 of the organs of the electric fishes. 



How does Electricity excite Nervous Phenomena. Let us 

 examine, lastly, how electricity can excite nervous phe- 

 nomena. The excitability of the nerves can also be 

 awakened, and sensations and muscular movements deter- 

 mined, by other agents as well as by electricity ; namely, 

 by heat, mechanical and chemical actions. Ought we to 

 conclude from these facts, that mechanical, chemical, and 

 calorific action, affect the nerves after they have been trans- 

 formed into the electric current ? We have no evidence 

 in favour of such an hypothesis ; if, however, notwith- 

 standing this, we would assume an analogous change, there 

 would perhaps be some appearance of probability of it in 

 the case of chemical actions ; but none for mechanical and 

 calorific actions. There are no circumstances, in fact, un- 



* Mr. Grove (On the Correlation of the Physical Forces, p. 49, 1846,) 

 has suggested, that " muscular force, animal and vegetable heat, &c., 

 might, and at some time will, be shown to have similar definite correla- 

 tions" to those which he has shown to exist between the forces of the in- 

 organic world. 



