RESPIRATION 219 



French writers on the subject have put it, ' Payment is 

 only made on coming out.' 



The effect on the lungs of breathing compressed air 

 is to cause them to expand downwards, the liver and 

 diaphragm being depressed so as to occupy the space 

 obtained by the compression of the gases in the stomach 

 and intestine. At the same time, the circumference of 

 the chest is increased and the number of respirations 

 lessened. By frequent repetition of exposure to com- 

 pressed air these effects may become permanent. 



In medicine, compressed-air baths have been used in 

 the treatment of emphysema. Favourable results have 

 been reported in many cases, results which, when one 

 considers the state of the lungs in emphysema, it is very 

 difficult to explain. One would have expected, indeed, 

 that their effect would have been to aggravate the con- 

 dition, for what is emphysema but overdistension of the 

 lung? In the subjects of this disease, however, the 

 physical effects of compressed air on the lung seem to be 

 exactly the reverse of those produced in health, the 

 diaphragm being raised instead of lowered, and the 

 circumference of the chest diminished, not increased. 

 The explanation of this apparent paradox is not forth- 

 coming. 



2. Tissue Respiration. 



In the days of Priestley (1772) it was held that 

 respiration and combustion were identical processes, that 

 compounds carried to the lungs were burnt up there by 

 oxygen, and carbonic acid formed from them, just as 

 happens in the combustion of a candle. When this 



