13-i ANNUAL OF SCIENTIFIC DISCOVERY. 



interrupted current, are displayed very simply by an arrangement of M. 

 Claude Bernard's, in which there are introduced into the same current, from 

 a small Cruickshank's battery, first, the nerve of a frog's leg, and second, a 

 delicate voltameter; the apparatus being so constructed that the current 

 may be cither continuous or intermittent. By this arrangement, says M. 

 Bernard, it is shown that 



" ' So long as the current is continuous, chemical effects are produced, and 

 the physiological effects are ' mils/ or at all events inappreciable. The facts 

 are that the water in the voltameter is decomposed by the current, whilst 

 the limb of the frog remains perfectly motionless. But immediately that, 

 by means of the interrupter, the current is rendered intermittent, everything 

 is changed; the decomposition of water ceases in the voltameter, and the 

 frog's limb becomes violently convulsed.' * 



" But this experiment, although it illustrates very aptly the broadly marked 

 difference between the effects of the continuous and intermittent current, by 

 no means exhausts the subject of that difference, nor does it accurately 

 represent all the facts. For the continuous current is not devoid of physio- 

 logic action, nor is the interrupted, under all the circumstances, incapable of 

 acting chemically. True, there is no visible contraction of the frog's leg; 

 but under certain conditions the irritability of the nerve is exhausted, and 

 under others it becomes increased. True, there is no sign of sensation in an 

 amputated frog's leg, but the continuous current can produce sensory ef- 

 fects ; for the proof of which let any one pass a continuous current through 

 his tongue or eyeballs; or, as Purkinje did, through the cars.t And further, 

 it is quite easy to produce permanent, i. e., tonic, contraction of a muscle 

 or group of muscles, as we have often done by a current of this kind; and 

 there is evidence to show that not only persistent contraction of muscles 

 maybe relaxed by such influence, J but that hypersesthesia may be reduced. 



" Here, then, we have evidence of four kinds of physiologic action due to 

 the continuous current, namely, the production of sensory effects, and also 

 of motor, as well as the relaxation of spasm, and the reduction of hypcrres- 

 thesia, the different manner in which the current acts being mainly due 

 to its intensity. 



" Other circumstances, however, influence the quality and degree of action 

 exerted, namely, the direction of the current. Generally speaking, the 

 transmission of a continuous current through a nerve, in the direction from 

 the centre to the periphery, exhausts the vital property of the nerve; 

 whereas a current passed in the opposite direction, i. e., from the periphery 

 towards the centre, increases the vital property. The former is termed 'di- 

 rect/ the latter ' inverse.' Again, the direct current acts more energetically 

 than the inverse in producing muscular contractions. This we have often 

 witnessed, when employing, for the purpose of experiment or therapeutic 

 application, an ordinary Cruickshank's battery, and so making use of the 

 initial current that its intensity could be regulated and measured by varying 

 the number of plates employed. Not only is the muscular contraction pro- 

 duced by transmitting a current from twenty plates, much stronger when 



* Lemons sur la Physologie et la Pathologie du Systems Nerveux, 1858, tome i. p. 

 151. 



t Rust's Magazin, bd. xxiii. p. 297. 

 J Remak, Medical Times and Gazette, May 8, 1858. 

 Becquerel, p. 97. 



