386 



SCIENCE PROGRESS 



TABLE III 

 Absohite Pressure 4 Atmospheres 



Allowing, therefore, for the difference between goats and men 

 in the respiratory exchange per unit of body weight, and con- 

 sequent rate of circulation, it would take about four hours for 

 a man's body to become for practical purposes saturated with 

 nitrogen in compressed air. This conclusion harmonises with 

 the experience of workers in compressed air. Parts in which the 

 circulation is rapid are certainly saturated in a small fraction of 

 this time, as indeed has been shown experimentally by Hill b}- 

 determining the amount of free nitrogen in urine secreted during 

 rapid diuresis.^ We think, however, that von Schrotter, who 

 calculated that saturation is nearly reached in man within about 

 twenty minutes, has at any rate made a great practical under- 

 estimate, both of the time needed for saturation and that needed 

 for desaturation. In making his calculation, he has treated 

 the body as if the circulation through all parts were the same, 

 whereas it differs very greatly in different parts. From the 

 point of view of caisson disease, the quickly saturating parts 

 cause little danger (except with almost instantaneous decom- 

 pression from very high pressure), as is shown both by the 

 practical experience of men working in compressed air, and by 

 the fact that it is extremely difficult to produce an}' symptoms 

 in small animals with a rapid circulation rate. It is thus the 

 slowly saturating parts of the body which are of most practical 

 importance. Another source of error is that, as was shown by 

 Dr. Vernon,- of Oxford, in connection with our experiments, fat 



* Proceedings of the Royal Society, vol. Ixxix. p. 366, 1907. 

 2 Ibid. 



