294 ELECTEO-PHYSIOLOGY. 



soldered together at one extremity, and I touch the frog with the other and free 

 extremities of the pair. If I touch the nerves the whole frog is strongly cou- 

 ti'acted, and is equally so when I touch a nerve and muscle; while, on the other 

 hand, if the surface of the muscle alone be touched with the two extremities there 

 is only a slight contraction in the portion of muscle interposed between them. 

 The greater effect in the first case evidently results from the fact that the cur- 

 rent, and consequently the excitation, is conveyed by the nerves into the whole 

 muscular mass in which those nerves terminate. We thus arrive at a compre- 

 hension of the special effects of the so-called electric shock. 



It is well known that the pain is only felt at the articulations, or at least that 

 it is strongest at those points, and that when the quantity of electricity is in- 

 creased, the pain is not felt alone at the joints of the fingers, but reaches to the 

 articulation of the hand and arm. The shock increases if the hand with which 

 the jar or battery is touched be wet, and diminishes if it be dry ; in the former 

 case the skin conducts electricity much better then when it is deprived of mois- 

 ture. When a chain of persons is formed by contact of hands, those stationed 

 at the extremity experience the greater shock. These various effects are readily 

 understood through the principles of the propagation of electricity. It should 

 be also remarked that the electric conductibility of the muscular substance is 

 not less than five or six times greater than that of the nervous matter; and this 

 is intelligible because the muscle is full of blood, and consequently of serum and 

 saline solutions, while much solid matter enters into the constitution of the nerve. 

 When electricity is discharged through the hands and arms the section of the 

 conductor is narrowed at the joints where the muscular mass is smaller, and the 

 electrical density in the nervous fibres at those points is much greater than in the 

 same fibres imbedded in a large muscular mass : hence the shock and greater pain 

 in the articulations. Franklin exhibited to his auditors an experiment which is 

 explained in the same way. He caused the discharge of a strong battery to pass 

 through a living rat when wet, and the animal was not injured; but when the 

 rat Avas dry the same discharge killed it. There have been cases in which preg- 

 nant women have been killed by lightning without injury to the foetus. Under 

 both these circumstances the stratum of water served to conduct the electricity 

 and protected the foetus and the rat. 



These general remarks being premised, and before proceeding to an exposition 

 of the fundamental propositions of electro-physiology, it is proper that I should 

 say a word of the apparatus of measurement applied to these phenomena. 



Till recently those who studied electro-physiology contented themselves with 

 saying that the shock produced by the discharge of the jar, or by the current, 

 was more or less strong; that the frog was convulsed in a greater or less degree. 

 We have now an apparatus of measurement which we call a dynamometer. Let 

 us take a muscle, the gastrocnemius for instance of a frog, and fasten it by one 

 extremity to a hook or pin; at the other extremity let us suspend with a hook 

 a small weight of a gram or half a gram. When a current is passed into 

 this muscle there is a momentary contraction of the latter, and the weight is pro- 

 portionally raised. This is the force of the muscular contraction, which is com- 

 puted as is that of steam or falling water, from the product of the weight by the 

 space or height to which the M^eight was raised. It is necessary, therefore, in 

 the first place, to measure this height. If we would render the elevation more 

 conspicuous, resort may be had to an expedient which was once practiced in 

 physical investigation, the movement may be made more extensive by means of 

 wheels or a lever. But this procedure is now generally discarded, the direct meas- 

 urement by which the movement is not altered being preferred, and this is ob- 

 tained by the employment of small telescopes provided with micrometers. To 

 render the movement of contraction visible at a distance I use a very light lever 

 with very unequal arms. The end of the long arm moves over a graduated quad- 

 rant, and to the end of the short arm is fastened the leg of the prepared frog ; the 



