VITAL FORCE. 9 



thought, every sensation, is accompanied by a change in 

 the composition of the substance of the brain. 



In order to keep up the phenomena of life in animals, 

 certain matters are required, parts of organisms, which 

 we call nourishment. In consequence of a series of 

 alterations, they serve either for the increase of the 

 mass (nutrition), or for the supply of the matter con- 

 sumed (reproduction), or, finally, for the production of 

 force. 



II. If the first condition of animal life be the assimi- 

 lation of what is commonly called nourishment, the 

 second is a continual absorption of oxygen from the 

 atmosphere. 



Viewed as an object of scientific research, animal 

 life exhibits itself in a series of phenomena, the con- 

 nexion and recurrence of which are determined by the 

 changes which the food and the oxygen absorbed from 

 the atmosphere undergo in the organism under the influ- 

 ence of the vital force. 



All vital activity arises from the mutual action of 

 the oxygen of the atmosphere and the elements of 

 the food. 



In the processes of nutrition and reproduction, we 

 perceive the passage of matter from the state of motion 

 to that of rest (static equilibrium) ; under the influence 

 of the nervous system, this matter enters again into a 

 state of motion. The ultimate causes of these different 

 conditions of the vital force are chemical forces. 



The cause of the state of rest is a resistance, deter- 



