54 Prof. J. Burdon-Sanderson. Relation of Motion in Animals 



Second Fundamental Experiment* 



The point to which I 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 shows that 



Photograph 6 * 



the .column rises at first abruptly, 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 tetanised (i.e., subjected to a frequent series of excitations) 

 corresponds 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 eircuit is so arranged that we can, without altering- 

 the resistance, project on to a second photographic plate the effect of 

 allowing a constant difference of potential to act on the mercury column 

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

 with the tetanus curve they are found to be nearly identical. 



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

 way as in the last instance for a succession of periods of one-fifth second, 

 alternating with equal periods of rest (Photo. 7). The complete cor- 

 respondence of the photographic curve with that represented in 



* Sartorius not cura^ised. Indirect excitation. The undulations on the line of 

 ascent indicate (he frequency of the stimuli — 60 per second. The radial line i 

 indicates here, not the moment of stimulation hut that at -which the short circuit 

 of the secondary coil was opened. 



