6 



ANIMAL MECHAKISxM. 



a single cause ; and thenceforth the number of forces which 

 were admitted diminished considerably. 



Weight and attraction were reduced to one and the same 

 force by Newton, who recognised, in the falling of the apple 

 to the ground, and the retention of the star in its orbit, the 

 effects of an identical cause — universal gravitation. Ampere 

 reduced magnetism to a manifestation of electricity. Light 

 and heat have long since been regarded as manifestations of an 

 identical force, an extremely rapid vibratory motion imparted 

 to the ether. 



In our own time a grand conception has arisen, once more 

 to change the face of science. All the forces of nature are 

 reduced to one only. Force may assume any appearance ; it 

 becomes, by turns, heat, mechanical work, electricity, light ; 

 it gives rise to chemical combinations or decompositions. 

 Occasionally, force seems to disappear, but it has only hidden 

 itself; we can find it again in its entirety, and make it pass 

 anew through the cycle of its transformations. 



Force, which is inseparable from matter, is, like it, inde- 

 structible, and to both the absolute principle, that in nature 

 nothing is created and nothing is destroyed, is applicable. 



Before we enter upon a detailed exposition of this great 

 conception of the conservation of force and its transformations 

 in the inorganic world, let us see whether any analogous 

 generalisation has been arrived at in the science of organised 

 bodies. 



The living being, in its manifestations of sensibility, intelli- 

 gence, and spontaneity, shows itself to be so different from 

 the inert and passive bodies of inorganic nature ; the genera- 

 tion and the evolution of animals are so peculiar to them- 

 selves ; that the earliest observers traced an absolute boundary 

 between the two kingdoms of nature. 



Particular forces were imagined, to which each of the 

 normal phenomena of life was attributed, while others, like 

 malignant genii, presided over the production of the maladies 

 by which everything that has life may be attacked. 



The complexity of the phenomena of life hindered observers 

 for a long time from discerning the link which united them, 

 and prevented their referring to one and the same cause these 



