VITAL FORCE. 9 



condition of life, and must be again renewed. Phy- 

 siology has sufficiently decisive grounds for the 

 opinion, that every motion, every manifestation of 

 force, is the result of a transformation of the struc- 

 ture or of its substance ; that every conception, 

 every mental affection, is followed by changes in the 

 chemical nature of the secreted fluids ; that every 

 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 organ- 

 isms, 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 consumed {reproduction), or, finally, for 

 the production of force. ^ 



II. If the first condition of animal life be the 

 assimilation of what is commonly called nourish- 

 ment, 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 

 connection and recurrence of which are determined 

 by the changes which the food and the oxygen 

 absorbed from the atmosphere undergo in the organ- 

 ism under the influence of the vital force. 



All vital activity arises from the mutual action 

 of the oxygen of the atmosphere and the elements 

 of the food. 



