NERVOUS ACTIVITY 509 



frog) contract. Galvani was right that there was such a thing 

 as animal electricity, but he was wrong in attributing muscular 

 contraction to it in such cases as those where there were contacts 

 of dissimilar metals ; Volta was wrong in denying the existence 

 of electricity of animal origin, but right in claiming that some 

 electricity was of metallic origin and was the true stimulus 

 in several cases in which Galvani thought it to be of animal 

 origin. 



It is only comparatively recently that the non-electrical nature 

 of nerve-impulses has been established. 



Albrecht Haller (1708-1777) brought the subject into the 

 domain of modern thought by distinguishing three things : 

 the inherent irritability of muscle (the vis insita), the nerve- 

 impulse (vis nervosa), and the stimulus to the muscle which 

 might or might not be the vis nervosa. Writing of the vis 

 nervosa he said : " It comes from without, and is carried to the 

 muscles from the brain by the nerves ; it is the power by which 

 the muscles are called into action." The vis nervosa, taking the 

 place of the succus nervens, remained in nerve physiology until 

 about the middle of the nineteenth century. 



Robert Whytt, of the University of Edinburgh (1714-1766), 

 though he furthered the study of reflex action, did not under- 

 stand nerve-impulses as clearly as did Haller with whom he 

 had a long controversy. Whytt denied to muscles inherent 

 irritability, and thought it was conferred on them by the nerves ; 

 he held that the stimulus could convey energy — a view now 

 rightly regarded as a neurological heresy. The controversy 

 lingered on until John Reid (1809-1849) demonstrated that 

 muscles severed from their nerves could, under suitable con- 

 ditions, retain their contractility for months. 



The suitable conditions were, (a) blood-supply for the muscles 

 and (b) their being constantly " exercised by Galvanism." Reid 

 in this way prevented the muscles showing atrophy from disuse. 

 He kept them in good condition by artificial, electrical instead 

 of by normal, neural stimulation ; but the irritability must have 

 been inherent in them in order that the stimuli should act on 

 them at all. The artificial stimuli could not have conferred 

 irritability on the muscles, neither, then, did the normal, neural 

 stimuli. The reception of nerve-impulses (neural stimuli) was 

 only the occasion of the muscles exhibiting the contractility 

 which they possessed independently. 



