ELECTRO-PHYSIOLOGY. 295 



spine of the frog is fastened above to another hook or to a pin. When the cur- 

 rent is passed into the himbar nerves, the muscles contract, the short arm of the 

 lever is raised, the long one moves in the opposite direction over a line 20, 50, 

 or 100 times longer than that described by the short arm ; that is, in the ratio 

 of their lengths. 



This movement is of course very rapid, and with the naked eye it would be 

 impossible to fix precisely the point at which the index arrives in the act of 

 contraction. For this reason Brequet, in a dynamometer which he constructed 

 for me some years since, placed before the index, and in contact with it, a light 

 ivory index, which the former pushed before it when the contraction occurred, 

 and which, when that had ceased, remained at the point to which it had been 

 carried. I repeat that, for precise measurement, it is necessary to read directly 

 the elevation or contraction of the muscle. We should, therefore, operate on a 

 single muscle, and not on a collection of muscles, such as are those which form 

 the members of a frog, because, as anatomists know, there are in the same 

 member some muscles which tend to raise the members, others to restore it to 

 its position, and whose effects partially neutralize each other. Nor to obtain an 

 exact measure does it suffice merely to use a single muscle, but this must be 

 formed of fibres all equally long and parallel among themselves, and such a 

 muscle, I think, is found under the tongue of the frog. For direct measure- 

 ment there must be fixed beneath the muscle a fine metallic cylinder, on which 

 the divisions are accurately marked, and this we observe with the telescope 

 furnished with a micrometer ; by which means we arrive at a rigorous deter- 

 mination of the elevation produced by the contraction. I should add that, to 

 succeed fully in the experiment, it is requisite that the muscle should be kept 

 tense, because it is raised vertically, but at the same time the strain should not 

 exceed a certain limit, lest it be too much stretched and its structure altered. 

 And to conclude what relates to the measurement of the contraction, I would 

 state that we may determine also the times corresponding to the various phases 

 of this movement. In effect, when the electric current passes through the nerve 

 there is a certain time needed for the nerve to become excited, then for the 

 excitation to traverse the nerve and reach the muscle ; the muscle next con- 

 tracts, and in a very brief space of time the contraction ceases and the muscle 

 is again relaxed. 



There is an ingenious method devised by Watt for measuring the velocity 

 with which the pistons of the steam-engine move, and it is this method which 

 I have used for ascertaining the duration of the muscular contractiout Let us 

 suppose a small brush attached horizontally, after having been dipped in ink, 

 to the muscle which is to be operated upon. It is obvious that if the point of 

 this brush touch lightly a card of blank paper it will describe, when the muscle 

 contracts and rises, a straight line on the card. But if the card be a disk 

 which has an uniform movement of rotation, we at once perceive that the line 

 will be no longer straight, but curved ; and that, knowing the velocity with 

 which the disk turns, we can, from the curve which is traced, deduce the time 

 occupied by the contraction and elevation of the muscle. In a word, the 

 length taken on the axis, called by geometers the abscissa, from the point at 

 which the pencil begins its course to the point which corresponds normally to 

 the vertex of the curve, determines the time which the disk occupies in de- 

 scribing this interval, and this time is that which corresponds to the duration of 

 the contraction. 



From many experiments it results that, in the first moments, when the vi- 

 tality of the muscle is still considerable, the duration of the contraction is ji^ of 

 a second ; the entire contraction, that is, the contraction and relaxation of the 

 muscle, occupies ^ or ^ of a second ; which implies that the period of relaxation 

 of the muscle is much longer than that of the contraction, strictly so called. 



