238 THE METABOLISM IN COMPRESSED AIR 



the alveolar oxygen tension works out as 680 mm. after deducting 

 tension of water vapour and C0 2 . The Hb is 96*5 per cent, 

 saturated at this tension that is, the blood contains 18-09 per 

 cent. 2 combined, it also contains 1'81 per cent, dissolved, in all 

 19-9 per cent. The difference between the two conditions is 4- 6 

 per cent. 2 . Now in the capillaries 8 per cent. 2 is used up, so 

 in the first case 7' 6 per cent. 2 remains over in the venous blood, 

 and 11-9 per cent, in the second case. In the first case the relative 



saturation of the venous blood is ^-,=40-51 per cent., corre- 



11*9 

 spending to IT mm. 2 tension ; in the second case ..-5-^7, = 63'44 per 



lo" / O 



cent., corresponding to 43 - 4 mm. 2 tension. Thus while the 

 alveolar 2 tension rose from 110 to 670 mm., the 2 tension in 

 the capillaries rose only 26 -4 mm. It takes about 3 atm. 2 to 

 make a relatively high 2 tension in the tissues (Zuntz and 

 Loewy). The continued action of oxygen above 100 per cent, of 

 an atm. acts as a poison, producing inflammation of the lungs and 

 convulsions. Very high pressures kill as if by asphyxia. 



J. J. R. Macleod and the writer have studied the respiratory 

 exchange in mice and rats placed in compressed air or oxygen. 

 The pressure chamber was fitted with thick glass windows and a 

 pressure gauge. The outgoing current of air was led through 

 sulphuric acid and soda lime absorption tubes, and the output 

 of C0 2 and H 2 obtained by weighing the tubes. From the re- 

 sults obtained we concluded that compressed air above 4-5 atm. 

 lessens the C0 2 output and lowers the body temperature of mice 

 and rats. This effect is not entirely due to the partial pressure of 

 oxygen, for 10 atm. of air is more depressing in its effect than 

 2 atm. of oxygen. There are other factors to consider, such as 

 the cooling effect of compressed air it is a better conductor of 

 heat and the resistance which highly compressed air may 

 establish to the diffusion of C0 2 from the alveolar air to the 

 tidal air. The saturation of the air with moisture which occurs 

 in pressure chambers helps to cool such small mammals as mice 

 and rats, but this can have no effect on men. Turning to the 

 study of the nitrogen output, we found that no noteworthy 

 change took place in dogs exposed for 7 hours to 8 atm. 

 of air. 



