IN THE ANIMAL ORGANISM. 213 



may assert, that no part of the momentum of force 

 is expended in maintaining their form and structure, 

 when their elements have once combined in that 

 order in which they become parts of organs endued 

 with vitality. 



Very different is the character of the azotised 

 vegetable principles ; for, when separated from the 

 plant, they pass, as is commonly said, spontaneously, 

 into fermentation and putrefaction. The cause of 

 this decomposition or transformation of their ele- 

 ments is the chemical action which the oxygen of the 

 atmosphere exercises on one of their constituents. 

 Now we know, that as long as the plant exhibits 

 the phenomena of life, oxygen gas is given off from 

 its surface ; that this oxygen is altogether without 

 action on the constituents of the living plant, for 

 which, in other circumstances, it has the strongest 

 attraction. It is obvious, therefore, that a certain 

 amount of vital force must be expended, partly to 

 retain the elements of the complex azotised prin- 

 ciples in the form, order, and structure which be- 

 long to them ; and partly as a means of resistance 

 against the incessant tendency of the oxygen of the 

 atmosphere to act on their elements, as well as 

 against that of the oxygen separated in the organ- 

 ism of the plant by the vital process. 



With the increase of these easily altered com- 

 pounds, in the flower and in the fruit, for example, 

 the sum of chemical force (the free manifestation 

 of which, counteracted by an equal measure of vital 



