1906.] Increased Barometric Pressure on Man. 



In another experiment the following were the results : — 



23 



Sample. 



Time and pressure. 



Percentage 



of 



nitrogen. 



Calculated N per cent., 



supposing urine 

 followed the pressure. 



1 

 2 

 3 

 4 

 5 

 6 





2-64 

 4 57 

 4-69 

 4-35 

 4-57 

 4-252 



1-1x4 = 4-4 

 1-1x4 = 4-4 

 1-1x4 = 4-4 

 1-1x4 = 4-4 

 1-1x4 = 4-4 

 1-1x3 = 3-3 



8 minutes later 



9 



„ 13 



23 



At 30 lbs. during decompression 



These results, amply confirmed by our other experiments (vide tables, 

 pp. 26 and 27), merit some consideration. 



First of all, we note that an exposure of more than five minutes to 

 a positive pressure of 30 lbs. is necessary in order to produce saturation; 

 the mean of five samples taken under these conditions is 1*99, as compared 

 with 3*3, the theoretical value. 



Saturation appears to be attained in 10 minutes,* however. Thus, the 

 mean of seven samples, taken not less than 10 minutes after attaining the 

 above-mentioned pressure, was 3*32. For a pressure of +45 lbs. the same 

 statement appears to hold, but the time limit is probably slightly lower, as, 

 on two occasions, full saturation was obtained in eight minutes. The mean 

 of eight observations at this pressure, for exposures of less than 10 minutes, 

 is 4*23, the theoretical value being 4*4. 



The next point to notice is that the escape of dissolved gas is a much 

 slower matter than could be expected. Thus, in experiments at +3 

 atmospheres, samples were taken when the pressure had fallen during slow 

 decompression to +2 and +1 atmospheres. The means of 7 and 8 

 observations at these pressures were, respectively, 3*63 and 2*75, i.e., the 

 samples were super-saturated. 



These results, however, are not surprising, since some of the urine taken 

 in the specimen must have been separated from the blood while under the 

 higher pressure, hence we could not assert, on the strength of these 

 observations alone, that any definite retardation occurs in the equilibrating 

 process. But, if we consider the analyses made after returning to the 

 normal pressure, we find very strong evidence in support of such a view. 

 In the experiment recorded above, a sample passed sixteen minutes after 

 decompression contained 2*373 per cent, of nitrogen, in another experiment 

 the amount was 1*66, the mean of 5 being 1-64. 



* Saturation of the kidney under the conditions of diuresis is probably far quicker than 

 that of other and less vascular organs. 



