FORCES AND ORGANS. 7 



manifold effects, and thus reducing the number of forces 

 which had at first been admitted. Man ended by taking 

 the fictions of his imagination for realities. Little by little, 

 the charm of the unintelligible exercising fascination over 

 him, he at last denied that physical laws had any in- 

 fluence upon living beings. This extravagant mysticism 

 represented certain animals as capable of withdrawing them- 

 selves from the influences of weight ; according to it, animal 

 heat was of another essence than that of our hearths ; subtle 

 and impalpable spirits circulated in the vessels and the nerves. 



Time has not even yet disposed of all these absurdities ; 

 but we can prove that the science of life tends at present 

 to undergo a transformation as complete as that of the phy- 

 sical sciences, whose development we have just sketched. 

 Physiology, guided by experience, seeks and finds the physical 

 forces in a great number of vital phenomena ; every day sees 

 an increase in the number of cases to which, we can apply 

 the ordinary laws of nature. That which escapes them 

 remains for us the unknown, but no longer the unknowable. 

 Among the phenomena of life, those which are intelligible 

 to us are precisely of the physical or mechanical order. 



In the living organism we shall fiud those manifestations 

 of force which are called heat, mechanical action, electricity, 

 light, chemical action ; we shall see these forces transforming 

 themselves one into the other, but we must not hope to arrive 

 immediately at the numerical determination of the laws which 

 regulate the transformations of these forces. The animal 

 organism does not lend itself to exact measurements, its com- 

 plexity is too great for valuations, to which physicists attain 

 with great difficulty by making use of the simplest machines. 



Each science, according to its degree of complexity, is 

 approaching more or less surely to the mathematical precision 

 at which it must arrive sooner or later. A law is only the 

 determination of numerical relations between different phe- 

 nomena; there is then no perfect physiological law. In the 

 phenomena of life it is scarcely possible to determine and to 

 foresee anything except the manner in which the variation will 

 be produced. Hitherto, the physiologist has reached only that 

 degree of knowledge which the astronomer would possess, who 



