CHAPTER X 



RESPIRATION 



PLANT RESPIRATION— RESPIRATORY ORGANS IN ANIMALS - 

 DUST AND SAND— HAEMOGLOBIN— ANAEROBES 



The breath of Heaven fresh blowing, pure and sweet, 

 With dayspring born ; here leave me to respire. 



Milton, Samson Agonistes, 



Plant Respiration 



With the inevitable exceptions, which will be considered 

 later, all animals and plants breathe, that is to say, they take 

 in oxygen and give out carbon dioxide; and unlike the taking 

 in of food, which is intermittent, respiration goes on all the 

 time. It is true that in green plants in daylight the process 

 is veiled by the fact that they take in as part of their food a 

 good deal more carbon dioxide than they breathe out, and 

 as a result of the metabolism or the breaking up of the com- 

 plex substances which build up the cells and the tissues they 

 excrete more oxygen than they take in through breathing. 

 We have in plants two systems working "contrariwise," as 

 Tweedledee would say: (1) the breathing, which works day 

 and night in the light or in darkness; (2) the feeding, which 

 works only in green plants in daylight. 



Life is a slow combustion: just as a steam engine is enabled 

 to move about and maintain a high temperature by the 

 combustion of coal, which requires the presence of oxygen — 

 for without this gas burning does not take place — so in the 

 bodies of plants and animals the complex substances derived 

 from the elaboration of the food are gradually but very slowly 

 burnt up. The energy thus set free enables animals to move 

 about and, in certain cases, such as birds and mammals, to 

 maintain a fairly high temperature. But this movement and 

 this heat disappear as soon as the plant or animal dies.* They 

 are, in fact, attributes of living matter. 



7-2 



