SOME RECENT WORK UPON MUSCLE AND NERVE. 437 



constitutes its contraction. It is well known that the pheno- 

 menon may be studied in the excised muscle of a recently 

 killed cold-blooded animal such as the frog, for many hours 

 after the removal of the muscle from the body ; a rapid 

 shortening or twitch occurs in such excised muscle when a 

 single stimulus, preferably an induced current, is applied 

 either to the muscle or the nerve supplying" it. The study 

 of the muscular response upon its mechanical side received a 

 notable advance fifty years ago by the application of the 

 graphic method devised by Helmholtz. This involves the 

 attachment of one end of the excised muscle to the short 

 arm of a small lever ; since the other end of the muscle is 

 immoveably fixed by a suitable holder, the shortening 

 present during the twitch must move the lever and a longer 

 arm of this can by appropriate arrangements be made to 

 record its displacement upon a blackened surface moving 

 at a known velocity. The record thus obtained is known 

 to all physiological students as the muscle curve ; since the 

 rise of the lever with its subsequent fall is the agency which 

 has actually written the curve, the curve itself indicates the 

 successive positions which the lever has assumed at different 

 periods of time. 



The influence of various conditions upon muscular 

 activity have been studied by obtaining such curves and 

 noting what alterations are now present in the records. 

 In this way the intensity of the stimulus, the tempera- 

 ture of the muscle, the alterations due to increasing 

 mechanical load, the effects of previous muscular activity, 

 of chemical substances and of many other agencies have 

 been ascertained. In view of all this work it is a little 

 singular that a point of prime importance involving the 

 meaning of the record itself should have only come to the 

 front recently. The muscle curve is the history of the 

 movement of the lever to which the muscle is attached, 

 and obviously this derives its value on the supposition 

 that we may deduce from the movement of the lever, 

 the mechanical change which occurs in the muscle. Does 

 a light lever of the type described faithfully follow the 

 muscular shortening? Is it a reliable historian or has it 



