1906.] Increased Barometric Pressure on Man. 25 



It must be admitted that these observations indicate in a manner not 

 to be disregarded the extreme danger of rapid decompression from high 

 pressures. It might even be doubted whether 20 minutes per atmosphere 

 is an absolutely safe allowance ; indeed, a few fatal cases, recorded in the 

 literature of caisson works, in which this time appears to have been allowed, 

 support such a contention. It may well be, however, that a certain steepness 

 of pressure-slope between dissolved and free gas is necessary for the formation 

 of bubbles sufficiently large to produce injury. 



So far as our observations go, with a decompression rate of 20 minutes an 

 atmosphere the dissolved nitrogen falls in a given time to the same level, 

 whatever be the height of pressure attained during the experiment. That 

 is to say, the excess of dissolved nitrogen on returning to zero is no greater 

 after exposure to three atmospheres than after raising the pressure to two 

 atmospheres only. It would seem that the velocity of escape diminishes 

 from some critical point. If this be so, it would be an argument for retarding 

 the later stages of decompression in order that an equilibrium may be 

 re-established on returning to normal conditions. 



The causes underlying these results remain for subsequent consideration ; 

 in the light of other experiments we have carried out, we think it possible 

 that a physical explanation will be found adequate to account for the facts, 

 but our investigations are not yet sufficiently complete to permit its 

 immediate statement. 



A complete table of our analytical results is subjoined ; the figures queried 

 are possibly vitiated by experimental errors, we have no reason to doubt 

 the accuracy of the others. 



Our general conclusions from the present investigation are : — 



(1) The body fluids of man exposed to compressed air absorb nitrogen in 



accordance with Dalton's law. 



(2) Saturation of the body fluids is attained after exposure to pressures 



of +30 — 45 lbs. for from 10 to 15 minutes.* 



(3) Even with a decompression rate of 20 minutes an atmosphere, 



equilibrium between dissolved and atmospheric nitrogen is not 

 completed 15 minutes after decompression. 



* Our results agree in principle with those deduced by V. Schrotter from theoretical 

 considerations, vide ' Sauerstoff in der Prophylaxie und Therapie der Luftdruckerkrank- 

 ungen,' Berlin, 1904, pp. 35—39. 



