1906.] oil Compressed Air and its PJiysioJogical Effects. 371 



gravity have yet occurred. Nevertheless we have proved that the 

 workers have excess of nitrogen in their bodies after decompression. 

 We have given them a quart of beer to drink in the tunnel 

 oO minutes before decompression to provoke diuresis, and have made 

 them empty their bladders just before, and again 10 minutes after, 

 decompression. Their urine yielded more than the normal volume 

 of N2 (1*6 per cent, in place of 1*2 per cent.). The urine, passed 

 immediately after their decompression, obviously effervesced. 



The saturation of the body fluids with N.^ probably follows a 

 curve, at lirst steep in ascent and then slowing off. On decompression 

 the curve of desaturation is prol^ably the reverse — at first steep in 

 descent and then slowing off. Thus we find our urine not saturated 

 with N2 when we reach say + ?> atm., but becoming saturated in the 

 next 10 minutes. Again, we find on examining, that even after 

 allowing '10 minutes per atm. for decompression, there is more N2 

 than normal in our urine. Thus the urine secreted in the next 

 10 minutes following decompression may contain 1 • 6 to 2 per cent, 

 in place of the normal 1 • 2 per cent. 



The records of caisson works seem to show that bad ventilation of 

 the caissons increases the cases of illness. E. W. Moir, in particular, 

 has laid great stress on this, and has attributed caisson illness to 

 excess of carbon dioxide in the air breathed. Snell, the medical 

 officer at the Blackwall tunnel, accepted Moir's views, and said that 

 to avoid caisson illness it is necessary to keep the CO2 in the air under 



• 1 per cent., and this is actually being done now at the Rotherhithe 

 tunnel. To maintain so perfect a ventilation as that means an 

 enormous supply of compressed air, and entails great expense. The 

 vast hall at Rotherhithe full of compressor engines is a most im- 

 pressive sight. 



The work of modern physiologists is opposed to this view 

 (Haldane). Mr. Ham and I have exposed animals in compressed 

 air to a partial pressure of CO2, equal to 10 per cent, of an atm. 

 Mr. Greenwood and I frequently have no ventilation going in our 

 chamber, because we dislike the noise of the pump, and are decom- 

 pressed from air containing as much CO2 as 2 per cent, of an atm. 



1 have breathed comfortably for half an hour in Bamberger and 

 Bock's life-saving dress, wherein the CO2 rose to 3 per cent. No 

 harm can result from the breathing of percentages of CO2 far higher 

 than Snell's figure of • 1 per cent. 



Other sources of the ill results of bad ventilation must be looked 

 to. First and foremost is the possible pressure of carbon monoxide 

 (CO), in caissons where flare-lights, furnaces, and blasting charges are 

 used, or where low-flash oils are employed to lubricate the compressors. 

 CO has an affinity for hemoglobin 1;30 times as great as Oo, and a 

 very small percentage may have a marked effect. This effect may 

 not be manifest in the caisson where the partial pressure of O2 is high, 

 but may first become manifest on decompression. For Haldane has 



2 B 2 



