258 On the Effects of certain Physical and 



armed the five platinum wires with flat plates of platinum, 

 of about one-eighth of an inch in breadth, and with these we 

 made contact with the nerves. The effect was as we antici- 

 pated. The phenomena of energetic spasmodic and tetanoid 

 muscular contractions on breaking the Voltaic circuit, were 

 instantly reproduced. 



To the effects of dryness and moisture must therefore be 

 added those of the number of points of contact between the 

 conducting wires and the neiwes. How many other circum- 

 stances also demand attention ! the vigour, the sex of the 

 animal, the season of the year, &c. So much more difficult 

 are physiological than physical experiments and investiga- 

 tions. 



III. The Electrogenic Condition of the Nerves; and its 

 Discharge. 



In detailing the following experiments, I must necessarily 

 be rather diffuse ; but I shall endeavour, whilst I omit no 

 point of importance, to be as little so as possible. 



The reader will be prepared for the details of the experi- 

 ments, if I first call his attention to figures 1, 2, 3, 4, 5, and 

 observe, that if the Voltaic current be passed, in the manner 

 indicated by the arrows, through the nerves, no spasmodic 

 or tetanoid effect is observed on breaking the circuit in the 

 cases 1 and 5, the electrogenic effect of that current being 

 apparently diffused amongst the soft parts behind the nerves, 

 or at the junction of the thighs ; whereas, if the current be 

 applied, as represented in figures 3 and 4, for a sufficient 

 time, and broken, the most extraordinary and continuous 

 spasmodic or tetanoid conti'actions of the muscles of the 

 limb are produced by the discharge of the electrogenic con- 

 dition of the nerves, phenomena which as instantly cease on 

 recompleting the Voltaic circuit. 



Experiment 1. Having carefully prepared a frog as repre- 

 sented in fig. 3, we first caused the Voltaic circuit to pass 

 through the wires from a to b, excluding the nerves, during 

 15 minutes, thinking we might induce the electrogenic state 

 in the spinal marrow ; but we had no spasmodic movement 

 on breaking the circuit, the Voltaic influence having doubt- 



