382 PHYSIOLOGY. 



and energy it has united with the carbon of the tissues to form carbonic 

 acid and with the hydrogen to form water. That which is not used up 

 at once constitutes a reserve supply in the tissue to be used as occasion 

 demands. 



It has been ascertained that the quantity of oxygen absorbed 

 within a given time is not found entirely in the carbonic acid exhaled 

 by the animal during the same time. Consequently one can scarcely 

 consider the oxygen as employed solely in burning carbon or in form- 

 ing carbonic acid. Thus, animals draw from the surrounding atmos- 

 pheric medium a quantity of free oxygen which attacks the ternary 

 and quaternary materials of the organisms. These then exhale car- 

 bonic acid and water as the result of the respiratory combustion. As 

 an animal can keep its weight the same during these combustive 



Air Inspired. Az Nitrogen. Air Expired. Az Nitrogen. 



Fig. 140. (LANGLOIS.) 



changes, it must be admitted that the carbon, hydrogen, and nitrogen 

 thus lost must be unceasingly renewed by the materials it ingests and 

 digests. 



It is impossible to observe any constancy in the quantity of the 

 products consumed or exhaled while searching into the amounts of 

 oxygen absorbed and carbonic acid given off by man in a certain 

 time. The chemical phenomena of respiration are, in fact, of such 

 extreme changeableness, due to a variety of causes, that physiolo- 

 gists can scarcely know them all. 



The expired air is richer in C0 2 than inspired. It contains 4.38 

 volumes per cent, of this gas, and consequently a hundred times 

 more C0 2 than the air inspired. 



The air expired is poorer in oxygen. It contains 16.03 volumes 

 per cent, of this gas, which is about 4.78 volumes per cent, less than 

 the inspired air. These figures show that the absorption or loss of 

 oxygen is greater than the elimination of C0 2 This further sub- 

 stantiates the statement that all of the oxygen absorbed does not 

 appear in the form of carbonic acid. 



