300 ELECTEO-PHYSIOLOGY. 



of caloric transformed into living force. From numerous accordant experiments 

 a quantity has been found which is called the equivalent of heat. This quan- 

 tity, which is about 420 kilograms, signifies that when a body of that weight 

 falls from one metre of height to the ground, this movement, or rather this quan- 

 tity of labor, is not extinguished, but is converted into a quantity of heat capable 

 of raising the heat of a kilogram of water by one degree centigrade, and that, 

 vice versa, this quantity of heat may be transformed into the mechanical labor 

 expressed by 420 kilograms. 



I must not omit to mention the experiment which incontestably demonstrates 

 the transformation of the living force into heat, an experiment which we owe to 

 the genius of Davy. During a very cold season, when the temperature of the 

 air was several degrees below 0°, he conceived the idea of causing two disks of 

 ice to rotate in contact with one another. Of course a greater force was neces- 

 sary to produce this rotation when the disks were in contact, and then both were 

 foimd to be in part melted and converted into water. The heat thus developed 

 could be notliing else than the living force consumed in the action of attrition. 

 Another striking example of this transformation is constantly going on in nature; 

 the water which falls from the clouds and which descends from the mountains 

 to the main, producing so great an amount of labor, is nothing but the solar heat 

 ti"ansformed. 



This principle once admitted, it becomes necessary to extend it to the battery 

 and to electro-magnetic motors, and finally, also, to the animal mechanism. The 

 chemical action which takes place in the interior of the battery is a combustion, 

 and whether it arises without development of a current, or when there is a cur- 

 rent, the quantity of heat developed will be always constant, and only the seat 

 of it will be changed, because the current transports that heat into various parts 

 of the circuit. If we have an electro-magnetic motor, or a machine which pro- 

 duces a certain quantity of labor, and in which a certain quantity of zinc is 

 burned, it will be found that when the machine is not at work there is developed 

 in the circuit and in the battery more heat than when it is in action, and that 

 the difference is just equivalent to the labor produced according to the quantity 

 which we have given. 



This digression was necessary to the conclusion which I would draw from our 

 electro-physiological experiments, and it is time to return to that which we were 

 making with the frog. 



I have said that it is possible to determine the quantity, however minute, of 

 the zinc which is oxidized in that evanescent moment in which the circuit with 

 the two springs remained closed. By making this experiment with care we can 

 ascertain the mechanical labor produced by the contraction of the frog — that is, 

 the product of the weight raised and the height. We can make the apjdication 

 of the mechanical theory of heat to this case, by inquiring whether the zinc con- 

 sumed in that instant of time develops a quantity of heat, and hence a quantity 

 of mechanical labor equivalent or equal to that produced by the muscle. In this 

 calculation it is assumed that the current which excites the nerve is transformed 

 entirely into muscular contraction, and yet in reality it is not so, because the 

 whole voltaic circuit is heated, and in the act of contraction the muscle also is 

 heated. Upon that calculation, however, it would result that the mechanical 

 labor of the contraction is, according to the theory, the same given, or rather a 

 little less than the equivalent of the heat developed by the zinc oxidized in the 

 battery. On the contrary, through the numbers deduced from rigorous experi- 

 ments an opposite result is arrived at ; the labor produced by the muscular con- 

 traction is at least twenty-five or thirty thousand times greater than that which 

 would correspond, according to the mechanical theory of heat, to the quantity of 

 zinc or to the current by which the nerve was excited. 



This result necessarily involved a conclusion which experiment has plainly 

 confirmed, and which serves greatly to enlighten our ideas on the properties of 



