636 EVOLUTION OF HEAT, LIGHT, AND ELECTRICITY. 



very remarkable nature, which influences both its intensity and its direction ; 

 this, according to M. du Bois-Reymond, is the existence of a thin layer of 

 muscular substance, beneath the tendinous expansion, whose electromotive power 

 is exactly opposite to that of the rest, so that its action tends to reverse the 

 general law of the muscular current. For when the gastrocnemius of a frog is 

 placed between the two electrodes, so as to touch them only with its tendinous 

 extremities, it gives a weak upward current; but if the frog have been previously 

 cooled, there will probably be no current at all; or if it have been frozen, there 

 may actually be a current in the opposite direction. If, now, a drop of any 

 liquid capable of corroding the muscular tissue (such as alcohol, creosote, acids, 

 alkaline solutions, &c.), be placed upon the aponeurosis- of the tendo-Achillis, 

 the ordinary upward current of the muscle is evolved ; and the same effect is 

 produced by completely removing a thin layer of muscular substance at the 

 natural transverse section. This effect is accounted for by M. du Bois-Reymond, 

 on the supposition that, at the tendinous extremities of the muscular fibres, the 

 linear series of peripolar elements is terminated by a single dipolar element, 

 whose positive pole is thus free, instead of the negative pole being so ; and he 

 has shown that by an apparatus of zinc and copper, constructed after this plan, 

 all the electric phenomena of the muscle at rest may be imitated. 



670. That a change in the electric state of a muscle takes place in the act of 

 contraction, had been ascertained by the experiments of Prof. Matteucci ( 330); 

 but, as he was only able to detect this by the galvanoscopic frog (the galvano- 

 meter which he employed not giving unquestionable indications of it), he was 

 not able to determine its nature with accuracy. This has been accomplished, 

 however, by M. du Bois-Reymond, who has shown that during contraction the 

 muscular current is not increased (as supposed by Matteucci), but is diminished 

 and even reduced to zero. In order to exhibit this phenomenon satisfactorily, 

 it is found advantageous to cause the muscle to contract powerfully or unin- 

 terruptedly for as long a time as possible, that is, to tetanize it ; and this may 

 be effected by acting violently on its nerve by heat, chemical agents, or a 

 succession of electric shocks ; or by poisoning the animal with strychnia. In 

 whatever mode the tetanized state is induced, the same result follows ; the 

 needle of the galvanometer passes over to the negative side. This, however, 

 does not indicate (as might be at first supposed) the development of a new current 

 during the contraction, in a direction opposite to that which prevails during rest; 

 but it is the consequence of the " secondary polarity'' 1 which is evolved in the 

 platinum electrodes, as soon as the muscular current is diminished ; the needle 

 passing from the positive to the negative side, as soon as the current of the 

 secondary polarity becomes more powerful than the original muscular current. 

 This negative deflection of the needle at the moment of contraction is always 

 proportional to the actual intensity of the current of the muscle while at rest ; 

 and it ceases as soon as the tetanic contraction ceases, after which the muscular 

 current gradually recovers its previous intensity. Thus, then, it appears that 

 the contraction of a muscle is attended with a marked diminution of its 



1 When the electromotor body is removed, and the two electrodes (platinum plates 

 immersed in a saturated solution of common salt) are connected by some imperfectly 

 conducting body, a secondary current is manifested in the reverse direction to the first, 

 the needle being deflected to the other side; this is caused by the electro-chemical reaction 

 of the substances which the current of animal electricity has evolved on the platinum 

 plates by means of its electrolytic action ; and its occurrence is often a useful and valuable 

 confirmation of the first result, as showing that the primary deflection really was the 

 consequence of the presence of an electromotor. When the electromotive action, moreover, 

 is very weak, it may be made more evident by reversing the position of the electromotor, 

 without first replacing the connecter ; so that the action which it will then exert in the 

 reverse direction will be strengthened by the secondary current developed by the previous 

 action. 



