LECT. IVX. XV. INDUCED CONTRACTIONS. 263 



der which we obtain a current by merely dividing a body. 

 It is impossible to establish a comparison between a muscle 

 and a thermo-electric body. In all these actions we can 

 only see various causes of molecular movement. 



We, may, however, ask ourselves this question, Does 

 the cause of nervous phenomena reside in these molecular 

 movements of the substance of the nerves, or is it owing 

 to a disturbance in the equilibrium of the ether, distri- 

 buted in the nerves ? Is this disturbance the consequence 

 of a particular movement of the ether, which should con- 

 stitute what we call the nervous fluid ? 



We can make no satisfactory reply to these important 

 questions ; the facts which are necessary to enable us to 

 resolve them are wanting, and will remain so, perhaps, 

 for a long time to come. Yet. if it be sometimes allow- 

 able, in scientific matters, to express, not only convic- 

 tions, but even doubts, I will not hesitate to tell you that 

 I do not consider it impossible to interpret nervous phe- 

 nomena, by the mere movement of the ponderable mole- 

 cules of nerves. 



But rather than stop to develop hypotheses, I believe it 

 will be more useful, before leaving the subject of the nervous 

 force, to dwell for some time upon two classes of phenomena, 

 or of the researches connected therewith. One relates to 

 the fact which I discovered, and named contraction by in- 

 duction, or induced contraction; the other relates to the deve- 

 lopment of the nervous force* 



Induced Contractions. By the term contraction by in- 

 duction, or induced contraction, has been expressed, in 

 England, a physiological fact which I discovered some 

 years ago. I shall henceforth employ this name, which has 

 the advantage of expressing briefly the phenomenon, and 

 of specifying in some respect its nature. 



I shall commence by briefly stating in what this pheno- 



