236 INFLUENCE OF ATMOSPHERIC PRESSURE 



I 



mi 



and compression of the gas in the alimentary canal, which leads 

 workmen to tighten their belts, and allows an ampler descent of 

 the diaphragm in inspiration. 



Paul Bert, by a remarkable series of experiments (La Pression 

 Barometrique, 1878), first proved that the true cause of compressed- 

 air illness is the effervescence of gas in the body fluids, an efferves- 

 cence which takes place when a man is rapidly returned to the 



normal atmospheric pressure. 

 The gas that is set free on 

 rapid decompression may ob- 

 struct the circulation in vari- 

 ous parts and produce one or 

 other of the protean symp- 

 toms which caisson workers 

 and divers suffer from. Gas 

 frothing in the heart may in- 

 stantly kill one man ; bubbles 

 in the heart or vessels of the 

 lungs, or in the respiratory 

 centre, produce embarrass- 

 ment of breathing in another ; 

 air embolism of the cerebral 

 vessels may cause aphasia, 

 mono- or hemi-plegia, of the 

 spinal vessels paraplegia; 

 bubbles in the joints and 

 aponeureses, or possibly in 

 the posterior nerve- roots and 



spinal cord, may cause the severe pains or bends from which 

 caisson-workers so frequently suffer, and a bubble set free 

 in the labyrinth of the ear explains the cases of audi- 

 tory vertigo. Lastly, bubbles may frequently form in un- 

 important places, such as the fat and glands, and produce 

 no symptoms. 



Bert also found that a high partial pressure of oxygen acts 

 as a general protoplasmic poison. It lessens the respiratory 



i This method was employed by C. Ham and the writer, and has shown us 

 that the bodies of rats, decompressed after exposure to 10 atm. of air, yield, 

 when cut up, about the theoretical amount of nitrogen gas i.e. the amount 

 calculated as dissolved, supposing 67 per cent, of their weight is water. Most of 

 the gas is free in the abdominal cavity and bowels. 



FIG. 12. Method of obtaining the 

 Gas set free in the Heart on Decom- 

 pression (v. Schrotter). 1 



