it CHANGE OF FORM IN MUSCLE DURING ACTIVITY 57 



this point the muscle lengthens slowly until it reaches its 

 original dimensions. The interval between the beginning of the 

 contraction and its maximum is known as the period of rising- 

 energy, that from the maximum to complete extension of the 

 muscle as the period of falling energy ; the entire period from the 

 beginning of the contraction to complete extension represents the 

 duration of the contraction. 



In regard to the amplitude, or height, of muscular contraction, 

 it must be remembered that there is generally a more or less 

 considerable enlargement in graphic records, and that the length 

 of the recording lever must always be taken into consideration, if 

 the real magnitude of contraction is to be determined. The two 

 stages of rising and falling energy may easily be determined if an 

 ordinate is drawn from the top of the curve, vertical to the abscissa. 

 As a rule the first is distinctly shorter than the second, but the 

 opposite may occur (e.g. on cooling). With regard to the form of 

 the contraction curve it must be remarked that in many instances 

 we cannot regard it as a complete expression of the process of 

 movement, since the recording lever is frequently arranged (apart 

 from possible spontaneous variations) so that its point describes 

 the arc of a circle in moving. The velocity of the travelling 

 surface has also a considerable effect upon the form of the curve 

 one and the same movement, recorded by the same lever, 

 yields very different curves, according as the inyograph plate 

 travels fast or slowly. 



I. DEPENDENCE OF THE PROCESS OF CONTRACTION UPON THE 

 NATURE OF THE MUSCLE 



The marked differences which exist in regard to the rate of 

 movement as manifested in different kinds of protoplasm, lead 

 us a priori to anticipate that similar distinctions must exist in 

 the muscles of different animals as well as in the different muscles 

 of the same species, as might be inferred at once from their fun- 

 damental differences of structure. And indeed the merest glance 

 shows that without considering other external influences yet to be 

 mentioned, the form and process of contraction are essentially 

 dependent on the nature of the muscle. Above all, we are im- 

 pressed by the enormous difference exhibited between smooth 



