504 



THE RESPIRATORY EXCHANGE 



a simple process of oxidation, the union of oxygen with carbon 

 and hydrogen to form carbon dioxide and water. This view 

 Regnault and Reiset contested, for they held that the oxidation 

 was a more complex process, in some respects complete, in others 

 incomplete, as shown by the discharge of such substances as urea 

 and uric acid. 



Within recent years many observers have carried out extensive 

 investigations to determine the influence of fasting and feeding 

 upon the respiratory exchange of men and animals, and upon 

 many points of interest have obtained concordant results. The 

 respiratory exchange shows a marked decrease, when no food is 

 taken, quickly reaches a minimum, and then remains remarkably 

 constant during a prolongation of the fast. In the case of the 

 fasting man, Ce.tti, the average absorption of oxygen was found 

 by Zuntz and Lehmann to be 4*65 c.c. per kilo body- weight and 

 minute for the third to the sixth day, and 4-73 c.c. for the ninth 

 to the eleventh day of this fast. Within twelve or twenty-four 

 hours of the last meal the respiratory exchange reaches the 

 minimum shown in the following table. 



The respiratory quotient falls during fasting to O75 or even 

 to 0*63 ; the animal is living upon its proteid and fat, which 

 contain a relatively large quantity of carbon and hydrogen and 

 a small quantity of oxygen. The lower figure is even below the 

 theoretical value for the combustion of fat, and is probably to be 

 explained by the formation of glycogen and sugar from the fat 

 and proteid of the tissues. The consideration of this question 

 can be rendered easier by the following formulae, which represent 

 the oxidation of different substances : 



