MOTION IN ANIMALS AND PLANTS. 343 



a g-reater tension in a continuous effort. Now, all these modifications 

 depend, so far as I have been able to ascertain, on diminution of the 

 rate of propagation of the excitator}^ wave. As has l>een alreadj^ 

 stated, w^e are able to measure this rate with great facility and accurac3^ 

 By alternately cooling and warming our chamber we can determine in 

 any number of instances the change of rate which a difference of 2°, 

 4^, or 6° C. produces, and compare the data so obtained with the 

 effects of the same changes on the duration of the monophasic varia- 

 tion and on that of the mechanical effort which it accompanies. 



Up to this point the phenomena we have had under consideration 

 have been associated with the response of a muscle to a single instan- 

 taneous excitation, i. e., the monophasic variation and the monetary' 

 contraction which it ushers in. We must now pass on to the consid- 

 eration of the electrical concomitants of those forms of contraction 

 which more obviously resemble the natural action of muscles. 



Physiologists have for half a century taught that natural muscular 

 action, whether reflex or vokmtary, is made up of single contractions 

 of definite duration, such as those we have been considering, i. e., of 

 a rhythmical series of such contractions of definite frequenc}-. This 

 doctrine — that voluntary motion is a well-organized system of twitches — 

 is now commonly expressed b}^ calling it a tetanus, a word which was 

 some fifty years ago diverted from its medical signification to be adopted 

 as a technical term in physiology, but not precisely in its present sense. 

 What is now meant by it is that every contraction, however continu- 

 ous it may appear to l)e, is in reality discontinuous. This conclusion 

 was arrived at by a method which, though sometimes of great value 

 to the physiologist, does not always lead to the discover}' of truth — 

 the method which consists in first imitating a natural process and then 

 mentally transferring the characteristics of the imitation process to 

 the natural process which it represents. In the present instance the 

 study of artificial tetanus has taught us a large proportion of what we 

 know as to the properties of muscle, but not much about vol untaiT 

 contraction. In assuming the identity of the latter with experinicntal 

 tetanus physiologists have perhaps minimized certain fundamental 

 difficulties and assigned undue value to certain analogies. 



Of the difficulties, the most obvious one is that discontinuity could 

 not. if it existed, be of any advantage. For if we regard the muscular 

 system as the mere instrument of the central nervous system and 

 every muscular fiber as the instrument of the motor cell which governs 

 it, it is difficult to see how subjecting that muscular fiber to a rhythm 

 of its own could have anv other effect than to interfere with its effi- 

 ciency. Of the analogies, the chief is, first, that just as when you 

 listen to a muscle in artificial tetanus you hear a musical sound of 

 which the frequency of vibration corresponds to that of the stimuli, 

 so a muscle when contracting vokmtarily gives out the (juasi-musical 



