152 rnYsiOLOGY of muscles and nerves. 



admitted that in such cases excitement does in reality 

 take place, but that it is not observable on account of 

 external circumstances (hindrance to the propagation to 

 the muscle), then these exceptions may be said to be 

 merely apparent. Moreover, assuming that the changes 

 in the strength of the currents within the nerve only 

 excite in consequence of the fact that they bring about 

 changes in the molecular condition of the nerve, and 

 combining with this all that we know of the effect of 

 other forms of nerve irritation, the following law regard- 

 ing nervous excitement may be regarded as the final 

 result : — 



Excitement of the nerve depends on a change in 

 its molecidar condition. It occurs as soon as such a 

 change is effected ivith sufficient speed. 



It may be added that this law is in all essential 

 points true also of muscle. But it appears that the 

 molecules of muscle are more sluggish than are those 

 of nerve, so that in the former very transient influences 

 may more easily be without effect.* 



> See Notes and Additions, Nos. 7 and 8. 



