MODERN ASPECTS OF THE LIFE-QUESTION. 755 



by chemical changes going on constantly in the substance of the mus- 

 cle, 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 

 electric discharge, by what mechanism is the contraction effected ? A 

 string of electrified masses, like a muscular fibril, would seem at first 

 to oppose the view now advanced. Such a row of particles would in- 

 deed attract each other when electrified and shorten the length of the 

 whole. But the force of contraction would increase as the length 

 diminished ; whereas the fact in the case of the muscle is precisely 

 the reverse. Two theories have been advanced to account for the 

 result. The first, proposed by Marey, likens the muscular fiber to a 

 string of india-rubber which, when stretched, contracts upon the ap- 

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

 other, brought forward and strongly supported by Radcliffe, explains 

 contraction by direct electric charge. Each fiber of the muscle to- 

 gether 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 fiber, lateral compression results from 

 the attraction of the electricities of opposite name, and, since the vol- 

 ume 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 when charged like a condenser. In this view of the 

 matter the normal condition of the muscle is one of charge, of elonga- 

 tion. Contraction results from the simple elasticity of the muscle 

 itself, the function of the nerve being only that of a discharger. 

 Whether this theory represents the actual fact or not, in all its details, 

 it is supported by the existence of rigor mortis, by the continued rel- 

 axation of muscle during the flow of the current, by the cessation of 

 contraction on the free access of blood, and by many other phenomena 

 otherwise difficult to explain. 



From this brief review, does it not seem probable that the phe- 

 nomenon of muscular contraction may be satisfactorily accounted for 

 without the assumption of " vital irritability," so long invoked ? May 

 it not be conceded that the theory that muscular force has a purely 

 physical origin is at least as probable as the vital theory ? 



Time would fail me to discuss the many other phenomena of the 

 living body which have been found on investigation to be non-vital. 

 Digestion, which Prout said it was impossible to believe was chemical, 

 is now known to take place as well without the body as within it, and 

 to result from non-vital ferments. Absorption is osmotic, and its se- 

 lective power resides in the structure of the membrane and the diffu- 

 sibility of the solution. Respiration is a purely chemical function. 

 Oxyhemoglobin is formed wherever haemoglobin and oxygen come in 

 contact, and the carbon dioxide of the serum exchanges with the oxy- 

 gen of the air according to the law of gaseous diffusion. Circulation 



