UTILIZATION OF ENERGY IN THE SODT. 289 



getting at each stage only a comparatively small amount of 

 heat evolved. By combining it first with one atom of oxy- 

 gen, we get aldehyde and water 



CsHeO + = CsEUO -f H 2 



1 Alcohol. 1 Oxygen. 1 Aldehyde. 1 Water. 



Then we add an atom of oxygen to the aldehyde and get 

 acetic acid (vinegar) 



+ = 



1 Aldehyde. 1 Oxygen. 1 Acetic acid. 



And finally we may oxidize the acetic acid so as to get car- 

 bon dioxide and water 



C 2 H40 2 + 4 = 2C0 2 + 2H 2 



We get, in both cases, from one molecule of alcohol, two of 

 carbon dioxide and three of water; and six atoms of oxygen 

 are taken up. In each stage of the gradual oxidation a 

 certain amount of heat is evolved; and the sum of these is 

 exactly the amount which would have been evolved by 

 burning the alcohol completely at once. 



The food taken into the Body is for the most part oxi- 

 dized in this gradual manner; the products of imperfect 

 combustion in one set of cells being carried off and more 

 completely oxidized in another set, until the final pro- 

 ducts, no longer capable of further oxidation in the Body, 

 are carried to the lungs, or kidneys, or skin, and got rid of. 

 A great object of physiology is to trace all intermediate 

 compounds between the food which enters and the waste 

 products which leave; to find out just how far chemical 

 degradation is carried in each organ, and what substances 

 are thus formed in various parts: but at present this part 

 of the science is very imperfect. 



The Utilization of Energy in the Living Body. In the 

 steam-engine energy is liberated as heat; some of the heat 

 is used to evaporate water and expand the resulting steam; 

 and then the steam to drive a piston. But in the living 

 Body it is very probable (indeed almost certain) that a 

 great part of the energy liberated by chemical transfer- 



