408 THE RESPIRATION 



sion has been properly controlled. This has been shown by Leonard 

 Hill in the case of the kidney. The " tissue" gas in this case can be 

 taken as the gas dissolved in the urine, by analyzing which, therefore, 

 at different stages of decompression, the excess of nitrogen over what 

 it should be at the external pressure, can be ascertained. On decom- 

 pression from + 30 pounds by two stages to zero, a considerable super- 

 saturation was found to exist. The excess of nitrogen can, however, be 

 cleared out of the kidneys rapidly and completely by breathing oxygen, 

 which should therefore be administered during decompression in cases 

 where great care has to be exercised (Leonard Hill). 



When symptoms do appear, they can, in most cases, be relieved by 

 recompression, and all modern caisson works are provided with a special 

 chamber for this purpose. We need scarcely say anything about this 

 treatment here, as its value is so well known. Suffice it to say that, 

 although it is most likely to afford relief when applied as soon as pos- 

 sible after the appearance of the symptoms, yet it is often efficacious 

 when applied several days after their onset. 



Quite apart from the dangers of decompression, it must of course be 

 remembered that the working conditions in a caisson are somewhat dif- 

 ferent from those at atmospheric pressure, as the air, owing to its com- 

 pression, is warmer and is loaded to saturation point with moisture. 

 This hot, wet air interferes with the heat-regulating mechanism of the 

 body, making hard muscular work very uncomfortable because of the 

 tendency of the body temperature to rise. The reaction of the body 

 against this tendency to hyperthermia consists in dilat'ation of the su- 

 perficial capillaries and increased heart action. 



When such working conditions are repeated day by day, the appetite 

 is likely to fail, partly because of the tendency of the body to suppress 

 the activity of the metabolic processes, so as to keep down heat produc- 

 tion, and partly, no doubt, because the digestive processes are working 

 below par on account of there being less blood circulating through the 

 visceral blood vessels, it having been sent to the surface of the body to 

 be cooled off. The worker therefore tends to take less food, his metabo- 

 lism becomes depressed, and his factors of safety against bacterial 

 infections become lessened. 



The risk of the appearance of symptoms on decompression is also 

 greater when the air in the caisson has been moist and hot, for the heart 

 has been overworking to maintain the bloodflow in the dilated vessels; 

 it gets fatigued and is consequently unable to maintain, during decom- 

 pression, a rate of bloodflow that is adequate for carrying the gas- 

 saturated blood to the lungs, where the excess of gas becomes dissi- 

 pated. 



