WORK UNDER PRESSURE AND IN GREAT HEAT 387 



takes up about six times as much free nitrogen as does blood. 

 The body fat thus forms a very large depot of nitrogen, which 

 greatly increases the time needed for saturation. On sudden 

 decompression of an animal saturated with compressed air the 

 fat becomes blown out with small gas-bubbles. 



We are in complete agreement with von Schrotter and Zuntz 

 as to the general form which the saturation curve of any part of 

 the bod}' must of necessit}- take, assuming the rate of circulation 

 to remain constant (see fig. i). For instance, a part which 

 takes one hour to become half-saturated will take two hours 

 to become three-fourths saturated, and three hours to become 

 seven-eighths saturated. During desaturation on decompres- 



20 30 40 50 60 70 80 90 100 110 120 

 Time in minutes. 



Fig. I. — Curve showing approximate rate of saturation of parts of the body 

 with an average rate of circulation and percentage of fat. 



sion, if no bubbles have formed to disturb the process, the 

 desaturation curve will be exactly the same. 



I now come to another point, as to which we have been led to 

 new and important conclusions. Practical experience of work 

 in compressed air shows that even with very rapid decompres- 

 sion no symptoms of caisson disease ever occur with an absolute 

 pressure of less than 2 atmospheres, and that symptoms are 

 very rare and slight until the pressure rises beyond 2'3 atmo- 

 spheres, or 19 lb. per square inch. This we found to be true 

 also for goats. Now if it is possible to decompress rapidly and 

 with safety from 2 atmospheres, or a little more, to i atmosphere, 

 it seemed likely that it would be possible to decompress with 



