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



Diminishing the frequency still further (to 14 per second) we obtain a 

 curve (Photo. 9) of which the character is that of a series of equal and 

 similar monophasic variations. 



We now go on to compare the variation-curve of artificial tetanus 

 with the nearest approach to a normal contraction we can obtain for 

 investigation, viz., the reflex response of the motor apparatus of the 

 spinal cord to an instantaneous stimulation of the cutaneous surface. 

 A ligature is applied as before to the tibial end of the Sartorius under 

 the distal contact ; but inasmuch as the muscle must now be excited 

 through its nerve, the proximal leading-ofF contact is on the hilus. 

 The mode of excitation is the same as before, but in this case the effect 

 has first to be communicated to the motor cells of the spinal cord 

 through the sensory apparatus, a process which occupies a relatively 

 considerable length of time. The motor cells then deal with it auto- 

 matically, responding to it in their own way, and inducing in the 

 muscles under their control an action which is the faithful and exact 

 expression of the changes going on in themselves. 



As is well known, it is not possible in a normal preparation to obtain 

 an unfailing response to an instantaneous stimulus applied to the 

 cutaneous surface, but the previous injection of a trace of a strychnine 

 salt (e.g., 1/30 milligram of the sulphate) is sufficient to give to the 

 motor apparatus of the cord the required degree of excitability. A 

 single induction current applied to the skin then evokes in the 

 Sartorius and other muscles, first a twitch which resembles the 

 response of the same muscle to a similar stimulus applied to its nerve ; 

 a little later, this twitch is replaced by a short, sometimes thrilling, 

 spasm resembling a short tetanus. What I have to show you is that, 



Photograph 9. 



The Reflex Electrical Response. 



