IS A SOURCE OF OXYGEN. 87 



formed from starch, sugar, or sugar of milk, that for 

 the same amount of carbon there must be separated 

 90, 100, and 110 equivalents of oxygen from these 

 compounds respectively. 



There is, therefore, but one way in which the 

 formation of fat in the animal body is possible, and 

 this is absolutely the same in which its formation in 

 plants takes place ; it is a separation of oxygen from 

 the elements of the food. 



The carbon which we find deposited in the seeds 

 and fruits of vegetables, in the form of oil and fat, 

 was previously a constituent of the atmosphere, and 

 was absorbed by the plant as carbonic acid. Its 

 conversion into fat was accomplished under the in- 

 fluence of light, by the vital force of the vegetable ; 

 and the greater part of the oxygen of this carbonic 

 acid was returned to the atmosphere as oxygen 

 gas.* 



In contradistinction to this phenomenon of vitality 

 in plants, we know that the animal system absorbs 

 oxygen from the atmosphere, and that this oxygen 

 is again given out in combination with carbon or 

 hydrogen ; we know, that in the formation of car- 

 bonic acid and water, the heat necessary to sustain 

 the constant temperature of the body is produced, 

 and that a process of oxidation is the only source of 

 animal heat. 



Whether fat be formed by the decomposition of 



* See Appendix, No. 19, on the formation of wax and honey 

 by the bee. 



