Notices respecting New Books. 227 



tected in the manner already described. Let this gap be closed by 

 the introduction of a cylindrical or prismatic piece of muscle, one of 

 the transverse sections of which is caused to abut against one of the 

 cushions, and the other transverse section against the opposite 

 cushion. The circuit is now complete, the muscle playing the part 

 of a little battery ; the galvanometer is included in the circuit ; and 

 if a current be produced, it will exhibit itself at the galvanometer. 

 In the above arrangement, however, no current is produced. Let one 

 of the ends of the muscle remain in contact with the cushion, as 

 before, and let the muscle be bent up and caused to rest with its 

 longitudinal section against the cushion ; a strong deflection is the 

 immediate consequence. The direction of this muscular current is 

 always from the transverse section through the galvanometer wire 

 to the longitudinal section ; and hence the law of action is, that 

 every point in the longitudinal section is positive to every point in the 

 transverse section. The current varies in intensity M^hen the points 

 of the muscle which come into contact with the cusliions are changed, 

 and the points of maximum and minimum action are determined in 

 a most delicate manner. The distinction between upward and down- 

 ward currents the author regards as non-essential ; in fact, it alto- 

 gether depends upon which end of the muscle is in contact with the 

 cushion whether the current is up or down. The part played by the 

 tendon is that of a passive conductor of the current generated in the 

 muscle itself. 



The author's experiments clear up the doubt which existed regard- 

 ing the influence of contraction on the muscular current. He proves 

 that, in the act of contraction, the muscular current is always dimi- 

 nished. A single contraction is unable to show any eflfect upon the 

 needle, on account of the inertia of the latter ; but when a continuous 

 spasmodic action is kept up, the effect becomes evident. The con- 

 vulsions may be obtained by gradually destroying the motor nerve, 

 by a chemical agent, by poisoning the animal with strychnine, by 

 passing a current of electricity of varying intensity through the 

 nerve, or by submitting the latter, by means of a break-circuit v.'heel, 

 to a series of successive shocks. From these experiments we select 

 the following one, as it is explanatory of another which has caused 

 some discussion among men of science. A live frog was taken and 

 one of its feet was dipped into a vessel containing a conducting liquid, 

 while the other foot was dipped into a second vessel of the same kind ; 

 the ends of the galvanometer wires were also connected with the 

 vessels. One leg was paralysed by having its ischiatic plexus cut 

 through. Tiie animal was then poisoned by strychnine, and convul- 

 sions were the consequence. Now in one leg these convulsions 

 diminished the muscular current, whereas in the passive leg no such 

 diminution took jjlace ; the equilibrium was therefore destroyed, and 

 a current exhibited itself on the galvanometer. 



It was this result that suggested the celebrated ex])eriment which 

 gave rise to the discussion before alluded to, — a discussion in which 

 the veteran Humboldt took the leading affirmative position. Du 

 Bois-Rcymond removed the frog's feet from the fluid and put his own 

 fingers in their place ; one arm he left passive like the paralysed leg 



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