MOTION IN ANIMALS AND PLANTS. 345 



while the curve rises to a lower level, the reason obviously being- that 

 the electrometer is acted on b}- a smaller number of excitations in a 

 given time. 



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

 a curve (photograph 9, PI. Ill) of which the character is that of a 

 series of equal and similar monophasic variations. 



THE REFLEX ELECTRICAL RESPONSE. 



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 excit(^d 

 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 relativel}^ 

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

 matically, responding to it in their own wa}^ 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 cuta- 

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

 salt (e. g. , one-thirtieth 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, although 

 the reflex spasm resembles a short artificial tetanus as regards the way 

 in which the muscle contracts, the contractions are shown by their 

 electrical concomitants to be of a diflferent nature. The strychnine 

 spasm, as it is rightly called, is seen not to be a tetanus, i. e., not to 

 consist of a series of single twitches, but to be a succession of contin- 

 uous contractions, the rhythm of which depends on the spinal cord, 

 not on the muscle. 



The grounds on which this conclusion is founded appear to me to 

 be unequivocal. The observation is a simple one. The automatic 

 mechanism, which carries the photographic plate, liberates as before, 

 at the beginning of the period of exposure, an induction current which 

 pricks the skin of the preparation. After an interval which may l)e 



