RESPIRATION 341 



gen, but of course take up a little oxygen and CO 2 from the sur- 

 rounding blood and tissue liquids. If they are formed in the blood 

 they tend to block the circulation on account of the great resist- 

 ance which they cause. Figure 82 is from a photograph of blood 

 vessels in the mesentery of a goat killed by rapid decompression, 

 and shows abundant bubbles in the veins. 



The bubbles are formed, not merely in the blood, but also in 

 the tissues outside it. We found that fat in particular is apt to be 

 very full of bubbles and thus become spongy. It had been found 

 by Vernon in connection with another investigation that gases 

 are much more soluble in oils than in water. In connection with 

 our investigations he determined the solubility of nitrogen in 

 body fats at blood temperature, and found that it is about six 

 times as great as in water. 2 The tendency of fatty substances to 

 act as a special reservoir of dissolved nitrogen is thus intelligible ; 

 and Boycott and Damant 3 afterwards showed that fat animals, 

 other conditions being the same, are considerably more liable to 

 symptoms of caisson disease than spare animals. Not only ordi- 

 nary fat, but the myelin sheaths of nerve fibers, will form reser- 

 voirs of dissolved nitrogen; and for this reason bubbles will tend 

 to be liberated in the white matter of the brain and spinal cord, 

 and inside the sheaths of large nerves. The "bends" and certain 

 other associated symptoms from which workers in compressed 

 air so frequently suffer are probably due to liberation of bubbles 

 from the gas dissolved in the myelin sheaths. It is difficult to un- 

 derstand otherwise the severe pain of "bends." Figure 83 shows 

 the positions of a large number of bubbles found in the white 

 matter at different parts of the spinal cord. 



The increased amount of nitrogen dissolved in the blood at 

 high atmospheric pressures was demonstrated by Paul Bert by 

 blood-gas analyses ; and Hill and Greenwood 4 not only confirmed 

 this, but showed that there is the same excess in the urine. Hill 

 and Macleod also observed directly the sudden appearance of 

 gas bubbles in the capillaries of the frog's web when the animal 

 was decompressed from a high atmospheric pressure. 5 



As a preventive of the occurrence of caisson disease Paul Bert 

 recommended slow and gradual decompression; but his experi- 

 ments in this direction were not very successful, as he had not 



2 Vernon, Proc. Roy. Soc., LXXIX, B, p. 366, 1907. 



3 Boycott and Damant, Journ. of Hygiene, VIII, p. 445, 1908. 

 *Hill and Greenwood, Proc. Roy. Soc., LXXIX, B, p. 21, 1907. 

 'Hill and Macleod, Journ. of Hygiene, III, p. 436, 1903. 



