[Chap. XVII RESPIRATION 151 



External evidence of respiration. We have frequently referred to the 

 fact that this chemically bound energy is liberated in the cells of plants 

 and animals by the oxidation of foods. The biological name for this 

 process is respiration. Perhaps most of us have at some time assumed 

 respiration to be synonymous w^ith the movement of oxygen and carbon 

 dioxide into and out of plants and animals. Such an inference is contrarv 

 to fact, and it should not be allowed to distort our thinking. There is no 

 more reason for confusing respiration with breathing, or with the en- 

 trance and outgo of oxygen and carbon dioxide, than there is for con- 

 fusing the process of eating with the subsequent chemical conversion 

 of food into protoplasm and cell wall substances in each cell of the plant 

 or animal body. 



The fundamental feature of respiration is the transformation of 

 chemically bound energy through the oxidation of foods within each 

 cell of the plant and animal body. The entrance of oxygen into a plant 

 and the escape of carbon dioxide from it are merely consequences of the 

 oxidation. In fact, we shall soon see that respiration ma\' occur without 

 the inward and outward movement of these two gases. 



The belief that the movement of these two gases is the essence of 

 respiration has further led to the wholly erroneous conclusion that 

 respiration in plants is just the converse of that in animals, or that it 

 occurs in plants only in the daytime or only at night. It should be obvi- 

 ous that this conclusion arises from a failure to distinguish between the 

 results of photosynthesis and those of respiration. It also arises from a 

 failure to distinguish between respiration and its external signs, which 

 are often used to detect the occurrence and rate of respiration. For in- 

 stance, in man and certain other animals, breathing and bodily tempera- 

 ture are well-recognized external evidences of respiration within the cells 

 of the body. Since the entrance of oxvgen into the body and the escape 

 of carbon dioxide from it are also external evidences of respiration, both 

 the occurrence and the rate of respiration may be measured by placing 

 the animal in a special calorimeter. In this apparatus the increase in 

 temperature and also the increase in CO2 and decrease in O2 can be 

 measured over a period of time. The dependence of man and other 

 animals upon food as the sole source of their supply of chemically bound 

 energy was discovered by means of such calorimeter tests. 



What external manifestations may be used to detect the occurrence 

 and rate of respiration in plants? Breathing, of course, need not be con- 



