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The Influence of Increased Barometric Pressure on Man. — No. I. 



By Leonaed Hill, F.E.S., and M. Greenwood, Jun., M.K.C.S. 

 Research Scholar of the British Medical Association. 



(Received January 16, — Read February 15, 1906.) 

 Introduction. 



The classical researches of Paul Bert, (1) confirmed in recent years by 

 v. Schrotter (2) and his co-workers, and also by Leonard Hill and 

 J. J. R. Macleod(3 and 4), have demonstrated beyond question that the ill 

 results observed in caisson workers and divers are to be attributed entirely to 

 injudicious rapidity of decompression. 



Experiments on animals have shown that every 100 c.c. of blood or tissue 

 fluid dissolve, at body temperature, about 1 c.c. of nitrogen under one 

 atmosphere of air ; 2 c.c. under two atmospheres ; o c.c. under three 

 atmospheres, and so on (Hill and Macleod, Hill and Ham). (5)* 



This nitrogen is set free as bubbles in the capillaries and tissue spaces when 

 the decompression period is made too short, and by the embolism of some 

 vessel, may produce symptoms varying in kind and severity. 



One of us (L. H.) having determined, by numerous experiments on animals, 

 that no ill effects follow exposure to pressures up to + seven atmospheres, if 

 20 minutes be allowed to each atmosphere for decompression, we determined 

 to investigate the effects of high pressures of air upon ourselves. 



The records of caisson works and the operations of deep sea divers show 

 that owing to the rapid rates of decompression at present employed by 

 engineers and divers, very great risk is incurred by workers in caissons at 

 pressures of +3 atmospheres, and by divers at depths of from 100 to 150 feet. 

 As, however, divers usually stop a very brief time, while caisson workers 

 outstay a shift of from 2 to 4 hours, the body fluids of the latter become 

 saturated with nitrogen, hence their greater danger at lower pressures. 



The limit for practical diving work is fixed by the great increase of 

 mortality and illness which occurs at depths much exceeding 100 feet, while 

 at less depths than this, accidents are by no means infrequent; being 

 occasionally very severe or fatal in character. 



The Admiralty set 120 feet as the limit of work for their divers, while the 

 most daring pearl and sponge fishers sometimes reach depths of 145 feet ; in 



* Bohr (' Nagel's Handb. d. Physiologie,' 1905, vol. 1, p. 117) gives the coefficient of 

 absorption of arterial blood exposed to an atmosphere of jST 2 , at body temperature as 1'26. 



