1906.] on Compressed Air and its Physiological Effects. 369 



may escape, owing to the small bulk of body, and great rapidity of 

 circulation, this lieing sufficiently rapid to clear oat the nitrogen. 

 Young animals also escape. After the decompression, the animals 

 show signs of sensations in the limbs, which they lick or bite at, 

 paralysis in the limbs follows, and then the animals fall over and 

 become unconscious. Xoise of gas bubbles gurgling in the heart 

 may be heard. Respiration becomes embarrassed, and the animals 

 die. On dissection, the peritoneal cavity may be found distended 

 with gas, or the stomach, and bubbles of gas may be seen in the 

 intestine. A part of this gas arises from the fermentative processes 

 of digestion, and from air swallowed during compression. The veins 

 of the portal system, the vena3 cavae, etc., are seen to contain chains 

 of bubbles : the heart is full of froth. Small hasmorrhages may be 

 present in the lungs. The edges of the lobes of the lung" are 

 emphysematous, blown out by the rapid decompression. The fat 

 everywhere is full of small bubbles, so too are the connective tissues. 

 Bubbles are seen in the joints, and may appear in the aqueous 

 humour of the eye. On opening the skull, bubbles are seen in the 

 veins of the brain. The bubbles are not restricted to the veins, but 

 may also be seen in the arteries. The coronary vessels of the heart 

 often show chains of bubbles. On microscopic examination, the 

 bubbles are seen in the capillaries ; here and there they run together 

 and form larger bubbles, sometimes rupturing the walls of the vessel, 

 and compressing the surrounding tissues. The bubbles appear in the 

 lymph spaces and lymphatics equally with the blood system. I have 

 never seen them actually within the substance of a cell. 



The gas set free in the heart can be collected and analysed ; about 

 80 per cent, of it is found to be nitrogen (Bert, v. Schrotter, Hill, 

 and Macleod). Catsaras lowered dogs in a diving dress to depths of 

 43 • 7 m., and after about an hour rapidly drew them to the surface. 

 He found bubbles set free in these dogs just as in those exposed in a 

 pressure chamber. In one dog which escaped without any severe 

 symptoms, gas bubbles were found in the veins six hours later. This 

 shows how long it may take for nitrogen gas once set free as bubbles 

 to escape from the lungs, and explains why caisson workers may 

 suddenly be seized some hours or more after leaving the works. In 

 such cases the bubbles may be swept from the abdominal veins — 

 where they do no harm^ — into the heart, and impede the action of this 

 organ, or they may penetrate the pulmonary circulation, and enter the 

 arterial system, and block up, perchance, the coronary arteries, or 

 others in the brain or spinal cord. 



Y. Schrotter placed an animal for 1 hour in 4 • 5 atm., and then de- 

 compressing it in 30 seconds, watched the appearance of bubbles in the 

 mesenteric vessels. Spasms occurred in 5 minutes (provoked by 

 bubbles in the spinal cord) ; visible bubbles appeared in the veins 

 2 minutes later. The blood is a colloidal solution, and it takes time 

 for the nitrogen to come out of solution and for the small bubbles to 

 YOL. XYIII. (Xo. 100) 2 B 



