470 MOVEMENTS. 



Changes in the Form of the Mitscular Fibres during 

 Contraction. It lias been found exceedingly difficult to de- 

 termine a question apparently so simple as that of the change 

 in form which the muscular fibres undergo during contrac- 

 tion ; and it is only of late years that this single point has been 

 definitively settled. The idea that the fibres do not shorten, 

 but that they assume a zigzag arrangement during contraction, 

 which was entertained by some of the earlier physiologists, 

 and was supported very strongly by Prevost and Dumas, 1 is 

 not adopted by any modern writers. All are now agreed, that 

 in muscular contraction there is an increase in the thickness 

 of the fibre, exactly compensating its diminution in length. 

 This has been repeatedly observed in microscopical exami- 

 nations, by Bowman, 3 Donne, 3 and many others ; and the 

 only points now to determine are the exact mechanism of 

 this transverse enlargement, its duration, the means by 

 which it may be excited, and its physiological modifica- 

 'tions. These questions, within the last few years, have been 

 made the subjects of elaborate investigations by Helmholtz, 

 Du Bois-Reymond, Aeby, Marey, and others ; and although 

 it is hardly necessary to follow these experimenters through 

 all of their investigations, many points have been developed, 

 particularly by the system of registering the muscular move- 

 ments, that possess considerable physiological importance. 



One essential condition in the study of the mechanism 

 of muscular contraction is to imitate, in a muscle or part of 

 a muscle that can be subjected to direct observation, the 

 force that naturally excites it to contraction. The applica- 

 tion of electricity to the nerve is beyond all question the 

 most perfect method that can be employed for this purpose. 

 We can in this way excite a single contraction, or, by em- 

 ploying a rapid succession of currents, can excite continuous, 



1 Journal de physiologic, Paris, 1823, tome iii., p. 301, et seq. 



2 BOWMAN, On the Minute Structure and Movements of Voluntary Muscle. 

 Philosophical Transactions, London, 1840, p. 488. 



3 DONNE, Cours de microscopie, Paris, 1844, p. 114. 



