84 THE FORMATION OF FAT. 



there must be separated 90, 100, and 110 equivalents 

 of oxygen from these compounds respectively. 



There is, therefore, but one way in which the forma- 

 tion 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 ele- 

 ments of the food. 



The carbon which we find deposited in the seeds and 

 fruits of vegetables, in the form of oil and fat, was pre- 

 viously a constituent of the atmosphere, and was ab- 

 sorbed by the plant as carbonic acid. Its conversion 

 into fat was accomplished under the influence 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 carbonic 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 

 fibrine and albumen, the chief constituents of blood, or 

 by that of starch, sugar, or gum, this decomposition 

 must be accompanied by the separation of oxygen from 

 the elements of these compounds. But this oxygen is 



* See Appendix, Note 19, on the formation of wax and honey by 

 the bee. 



