344 MOTION TN ANIMALS AND PLANTS. 



sound which Wollaston compared to the rum})h- of wheels over pave- 

 ment; the other analogy relates to the reflex spasm of strychnine, 

 which is not only rhythmical in itself, Imt is accompanied by a series 

 of electrical changes which are as rhythmical as if they were evoked by 

 a series of stimuli. The discussion of the muscle sound lies outside 

 of our present inquiry; the spasm of strychnine will be considered 

 after we have examined the electrical concomitants of artificial tetanus. 



SECOND FUNDAMENTAL EXPERIMENT. 



The point to which 1 have first to draw your attention is the form 

 of photographic curve which is obtained when the sartorius, injured 

 under one electrode by a ligature, is excited by a series of stimuli of 

 which the frequency is about 60 per second. The photograph (6 PI. II) 

 shows that the column rises at first abruptlv, but afterwards in such 

 a way that the rate at which it rises is at any moment proportional to its 

 distance from the point to which it will eventually arrive, i. e., to the 

 distance between the corresponding point of the curve and its asymp- 

 tote. The electrical state, therefore, which comes into existence when 

 a muscle is tetanized (i.e., subjected to a frequent series of excitations) 

 t^'orresponds to diagram 1. In other words, the electrometer is acted 

 on by the same difference of potential between its terminals through- 

 out, with the exception that the effect of the first, or first couple, of 

 excitations is often greater than that of the succeeding ones. Although 

 this hardly needs proof, it can be easily verified by direct experiment. 

 With this view our circuit is so arranged that we can, without altering 

 the resistance, project onto a second photographic plate the effect of 

 allowing a constant difference of potential to act on the mercur}^ cohimn 

 just as the plate is passing behind the slit. On comparing this curve 

 with the tetanus curve they are found to be nearh" identical. 



Let us now take the case in which a muscle is tetanized in the same 

 wa}' as in the last instance for a succession of periods of one-fifth sec- 

 ond, alternating with equal periods of rest (photograph 7, PI. III). The 

 complete correspondence of the photographic curve with that repre- 

 sented in diagram 2 indicates that the conditions corresjwnd with those 

 which are there theoretically represented. During each period of exci- 

 tation (tetanus) the movement upward of the meniscus is determined b}"^ 

 the difference of potential. During the intervals it follows in its fall 

 the similar curve of depolarization. 



From this we may now proceed to other forms of experimental teta- 

 nus in which the excitations are less frequent. Provided that the 

 frequency is not much less than 40 per second, the general contour of 

 the curve resembles the other one, with the exception that the effect 

 of each excitation is seen separately (photograph 8, PI. III). If the fre- 

 quency is diminished to 20 per second, the undulations are more ample, 



