302 NATURAL HISTORY OF ORGANIZED BODIES. 



That is to say that if, after the action of a muscle, the repose lasts one minute, 

 there "will have taken place a certain degree of restoration of the faculty of act- 

 in "• and that if the repose continues for two minutes, the restoration will not 

 have doubled the muscular energy. This likewise oilers a new analogy with 

 physical phenomena. In effect, a chilled body submitted to a source of heat, 

 gains much heat in the first few instants, and acquires but little afterwards in 

 proportion to the duration of the process of heating. 



Fifth law. — The habitual acfiviti/of a muscle and its nutrition stand in such 

 relation to one another that repose too much prolonged jiroduces atrophy of the organ, 

 u-hile action frcquenlli) repeated increases tlic volume of the muscle and augments 

 its aptitude to produce movement. 



Tlie examples which confirm this law are well known ; every one has had an 

 opportunity of observing the development of the muscles which, in some indi- 

 viduals, are more exercised than the rest, and, reciprocally, the atrophy of the 

 muscles which, for whatever reason, have been consigned to a long repose. 

 There are limits, however, beyond wliich this law ceases to be true; but these 

 limits have not yet been ascertained in a precise manner. 



The laws here stated regarding the muscular function are suflicieutly general 

 to enable us to recognize them in other functions which seem to have no analogy 

 with movement. Having incidentally mentioned the discharge of the torpedo, 

 I may here add that it would be interesting to inquire, within what liu^its the 

 laws above stated are verified in this order of phenomena. M. Brown StJquard 

 thinks, as I have before said, that they are governed by the same laws with the 

 muscular action ; but experiment has not yet succeeded in proving the reality of 

 this opinion, though it may be said to have every probability in its favor. The 

 onlv point on which perfect identity has thus far been established consists in 

 the fact that the discharges of the torpedo become weaker and weaker when a 

 series of them is provoked. There is, therefore, a real exhaustion of the function 

 simply by its own action ; a fatigue of the electric organ, as there is a fatigue 

 of the muscle. 



Tlie presence.' of blood in the organ and its ra])id circulation seem to be essen- 

 tial conditions for the abundant production of electricity and its prompt restora- 

 tion. Such, at least, is the conclusion which appears to result from the anatomy 

 of the electric apparatus of these animals, so richly provided with bloodvessels; 

 but the absence of exact means for appreciating the intensity of the discharges 

 of the torpedo has heretofore precluded rigorous experiment on this subject.* 

 We are able, however, as M. Moreau has shown, to verify the fact that a cessa- 

 tion of the current of the blood does not immediately prevent the electric appa- 

 ratus from operating, any more than it extinguishes instantly the contractility 

 of a muscle. But this suppression of the current of the blood would seem to 

 render the exhaustion of the electricity more rapid. 



It Avill be seen that there remain many desiderata in relation to the produc- 

 tion of electric phenomena in fishes. Tlie presence, however, of certain cliarac- 

 ters perfectly alike in the function of their electric apparatus and the muscular 

 function should iiuhice inquiry whether other analogies exist. It is thus that a 

 knowledge of the laws of a phenomenon traces for us the path to be followed in 

 the study of others, by indicating the most probal)le result of the researches which 

 may bo undertaken. 



M. A. ]\Ioreau has happily been led by the analogy which exists between the 

 production of electricity in the torpedo and the production of movement in the 



* The galvanometers which have been emploj'ed are too sensitive ; the electric discharge 

 Df the animal connnunicates to the needle so violent a deviation that it makes the circuit of 

 the dial-plate several times, and does not allow a comparison of the relative intensity of the 

 ditfereut commotions. It might be practicable, perhaps, by means of a circuit of derivation, 

 to give to the instrument only a part of the current, and as, in that case, the intensity of the 

 derived current remains proportional to that of the principal current, the variations of the 

 intensity of the discharge might probably be appreciated. 



