8 ANIMAL MECHANISM. 



knew, for instance, that the attraction between t\vo heavenly 

 bodies diminishes when their distance increases, but who had. 

 not yet determined the law of inverse proportionality to the 

 square of distances. Or, he is like the physicist who has proved 

 that compressed gases diminish in volume, but who has not 

 found the numerical relation bet\veeu their volume and the 

 pressure. 



Without doubt, however, there are numerical relations 

 between the phenomena of life ; and we shall arrive at the 

 discovery of them more or less speedily, according to the 

 exactitude of the methods of investigation to which we have 

 recourse. 



If physicists had limited themselves to establishing that 

 bodies dilate as they become heated, and if they had not 

 sought to measure the temperature of 'those bodies and the 

 volume which they assume with each variation of the temper- 

 ature, they would have had only an imperfect idea of the 

 phenomena of the dilatation of bodies by heat. For a long 

 time physiologists confined themselves to pointing out that 

 such or such an influence augments or diminishes the force of 

 the muscles, causes the rapidity of their motions to vary, 

 increases or diminishes sensibility and motive power. Science, 

 in our time, has become more exacting, and already the 

 rigorous determination of the intensity and duration of certain 

 acts, of the form of different movements, of the relations of 

 succession between two or several phenomena, the precise 

 estimation of the rapidity of the blood, or of the transference 

 of the sensitive or motive nervous agent; all these exact 

 measures introduced into physiology, lead us to hope that 

 from more scrupulous measurement better formulated laws 

 \\ill soon result. 



In the comparison which we are about to make between 

 the physical forces and those which animate the animal 

 organism, we shall take it for granted that the fundamental 

 notions recently introduced into science, and by which all those 

 forces tend to reduce themselves to one only, that which 

 engenders motion, are known; and shall, therefore, confine 

 ourselves to a rapid sketch of the new theory. 



The value of a theory depends on the number of the facts 



