No. 7.] AMERICAN ASSOCIATION. 387 



directly or stored up in the food. An animal, like a machine, 

 only transforms its energy. Lavoisier's guinea-pig, placed on 

 the calorimeter, gave as accurate a heat-return for the energy it 

 had absorbed in its food, as any thermic engine would have done. 

 But the parallel goes further. The mechanical work of an 

 engine is measured by the loss of its heat and not of its sub- 

 stance. So the mechanical or intellectual work of liviuo; beino-s 

 is measured by the amount of food rather than the amount of 

 tissue which is burned. The energy evolved daily by the human 

 body would raise it to a height of about six miles." 



The subject of muscular contraction is then discussed and 

 regarded as due to electric discharges generated within the 

 muscle itself and not carried to the muscle by the nerves. The 

 electrical charge which appears in the muscular fibre, may, it is 

 supposed, have its origin in so purely a physical cause as the 

 contact of the heterogeneous substances of which the tissue is 

 built up ; the maintenance of this charge being effected by 

 chemical changes going on constantly in the substance of the 

 muscle, by which the carbon dioxide is produced, which is shown 

 to be a measure of the work done. 



" Conceding now, that muscular contraction is of the nature 

 of an electi'ic discharge, by what mechanism is the contraction 

 effected ? A string of electrical masses, like a muscular fibril, 

 would seem at first to oppose the view now advanced. Such a 

 row of particles would indeed attract each other when electrified, 

 and shorten the length of the whole. But the force of con- 

 traction would increase as the length diminished ; whereas 

 the fact in the case of the muscle is precisely the reverse. Two 

 theories have been advanceed to account for the result. The first, 

 proposed by Marey, likens the muscular fibre to a string of 

 india-rubber which, when stretched, contracts upon the appli- 

 cation of heat, thus transforming heat directly into work. The 

 other, brought forward and strongly supported by Kadcliffe, 

 explains contradiction by direct electric charge. Each fibre 

 of the muscle, together with its sheath, constitutes a veritable 

 condenser, the charge upon the exterior being positive, and upon 

 the interior negative. When a charge is communicated to the 

 fibre, literal compression results from the attraction of the elec- 

 tricities of opposite name, and since the volume remains constant, 

 elongation is the consequence — precisely as a band of caoutchouc, 

 having strips of tin-foil upon its sides, may be shown to elongate 



