354 RESPIRATION 



It is probable that the bubbles first formed in supersaturated 

 blood and tissues are extremely small and comparatively harm- 

 less. One can observe the formation of these minute bubbles in 

 water which has stood in a pipe under pressure in contact with 

 air. When the tap is opened the water comes out milky with 

 minute bubbles, but no large bubbles are present. The smallness 

 of the bubbles leaves time to deal with cases of sudden decompres- 

 sion. Thus a diver who is blown up accidentally from a great 

 depth comes to no harm if he is sent down again at once or very 

 quickly got under high pressure in a recompression chamber. The 

 small bubbles already formed seem to go into resolution at once. 

 With any delay, however, the bubbles become larger and more 

 difficult to redissolve. In the diver referred to above bubbles had 

 evidently formed long before he reached surface and was recom- 

 pressed. 



In the case of workers in tunnels and caissons it is practically 

 very difficult, and undesirable in various ways, to keep the men 

 very long in an air lock during decompression. Another plan 

 seems much better, and has been partially carried out in recent 

 years in tunnels under construction at New York.^ The very high 

 pressures needed to keep the advancing face secure are only 

 employed in a section close to the face, this section being separated 

 from the rest of the tunnel by a steel air dam. If the total air 

 pressure in the advanced section is not more than 1%. times that in 

 the rest of the tunnel, the men can come through the air lock with- 

 out any delay. Let us suppose that the excess pressure is 35 lbs. 

 at the face and 7.5 lbs. in the rest of the tunnel. The total atmos- 

 pheric pressure is thus 50 lbs. at the face and 22.5 lbs. in the rest 

 of the tunnel. It is evident, therefore, that the men who have been 

 working at the face can come straight through either air lock, 

 even after very long shifts, provided that they are kept for a 

 sufficient time (fully an hour) in the low-pressure part of the 

 tunnel before coming through the second lock. If there were ar- 

 rangements for washing, changing, and meals in the low-pressure 

 section, this hour could be profitably employed. A six-hour shift 

 could be worked at the face, with an interval for a meal in the 

 low-pressure section, and there would be no blocking of the air 

 locks. The men could also go home at once, without the risk of 

 symptoms developing later. A plan of this kind, modified to suit 

 the varying conditions at different undertakings, seems to afford 

 the best means of solving the difficulties with air locks ; but exist- 



" Japp, Trans. Intern. Congress on Hygiene, Section IV, Washington, 19 12. 



