384 THE HUMAN BODY 



demonstrated. In view of these facts the physiological value 

 of deep breathing as a habit, so much insisted upon by certain 

 physical culturists, is, to say the least, problematical. 



The normal breathing mechanism is an adaptation by which 

 the blood is continuously provided with all the oxygen it is able 

 to carry, and by which also its carbon dioxid content, while 

 never allowed to become excessive, is kept high enough for the 

 proper performance of its hormone function. It would seem, 

 therefore, that before adopting a breathing habit different from 

 that established by nature one should require a very convincing 

 justification of the proposed change. 



Tissue Respiration. Our knowledge of the use of oxygen and 

 the production of carbon dioxid by the tissues is not very com- 

 plete. The following general facts may be stated here: (1) Al- 

 though the tissues take up oxygen from the lymph as fast as it is 

 brought by the blood they do not necessarily use it in oxidative 

 processes at the same rate; most of the oxygen appears to enter 

 some sort of chemical combination whereby it is stored until re- 

 quired by the tissues. (2) Tissue oxidations differ from ordinary 

 oxidative processes, such as occur when fuel is burned in a fur- 

 nace, for example, in that they are carried on through the agency 

 of enzyms known as oxidases. The chemical process of oxidation 

 carried on thus is not direct as in ordinary burning; it occurs at 

 a lower temperature, and requires a longer time; but it must be 

 remembered that the amount of heat produced by the oxidation 

 of a given weight of fuel is always the same whether the process 

 be rapid or slow, direct or indirect. Tissue oxidations, therefore, 

 are not necessarily wasteful because they go on indirectly and 

 slowly. (3) The amount of work that a man's organs do, is not 

 dependent on the amount of oxygen supplied to them, but the 

 amount of oxygen used by him depends on how much he uses his 

 organs. It is necessary to emphasize this fact because of the 

 notion, which seems to be rather wide-spread, that bodily proc- 

 esses are augmented by increasing the supply of oxygen to them. 

 The man who goes from his ill-ventilated office to the open coun- 

 try, and feels the impulse to vigorous exercise as he breathes the 

 pure country air, is apt to attribute his sensations of virility to 

 an imagined augmentation of all his bodily processes through the 

 increased amount of oxygen breathed in. The fact is that what- 



