IN THE ANIMAL ORGANISM. 195 



sistance to external, disturbing influences, to those of 

 heat, or of electricity, which tend to separate their 

 particles, as well as their power of overcoming resist- 

 ance in other compounds (of causing decomposition) ; 

 that, in a word, the active force in a compound de- 

 pends on a certain order or arrangement, in which its 

 elementary particles touch each other. 



The same elements, united in a different order, when 

 in contact with other compounds, exert a most unequal 

 power of offering or overcoming resistance. In one 

 form the force manifested is available (the body is ac- 

 tive, an acid, for example) ; in another not (the body 

 is indifferent, neutral) ; in a third form, the momentum 

 of force is opposed to that of the first (the body is 

 active, but a base). 



If we alter the arrangement of the elements, we are 

 able to separate the constituents of a compound by 

 means of another active body ; while the same ele- 

 ments, united in their original order, would have op- 

 posed an invincible resistance to the action of the 

 decomposing agent. 



In the same way as two equal inelastic masses, im- 

 pelled with equal velocity from opposite points, on 

 coming into contact are brought to rest ; in the same 

 way, therefore, as two equal and opposite momenta 

 of motion mutually destroy each other ; so may the 

 momentum of force in a chemical compound be de- 

 stroyed in whole or in part by an equal or unequal, 

 and opposite momentum of force in a second com- 



