1906.] Influence of Increased Barometric Pressure on Man. 447 



In no case have any severe after effects resulted. The maximum pressure 

 in our series corresponds to a water depth of 210 feet, which is 90 feet 

 beyond the limit fixed by the Admiralty for their divers. 



Supposing the special diving bell designed by one of us (L. H.) for the 

 slow decompression of divers were employed, it seems quite possible that 

 work might be carried out safely at a depth of 210 feet. Even a greater 

 depth than this might be attained by an intrepid man, for the limit appears 

 to be fixed by the pressure at which the toxic effects of high tension oxygen 

 become an immediate danger. 



These effects have been studied by Paul Bert, Lorrain Smith (10) and Hill 

 and Macleod (3). When the partial pressure of oxygen reaches 2 atmospheres 

 (corresponding to 10 atmospheres of air, or a depth of about 350 feet of water) 

 convulsions may occur in animals within 20 minutes. The limit of possible 

 safe working is therefore about 250 feet. Conceivably this limit might be 

 extended by diluting the air with nitrogen so as to lower the partial pressure 

 of the oxygen, but we do not claim more than that our experiments show 

 the safe diving depth may be increased up to 210 feet. 



The responsibility of those who allow short decompression periods in 

 caisson works is clear ; every death or case of paralysis from air embolism 

 must be set down to the negligence of the contractor. 



Next, as to the sensations we felt under pressure : the feeling of discomfort 

 in the ears and deafness, due to a difference in air pressure within and 

 without the tympanum, is too well known to need description. Owing 

 probably to a catarrhal condition, we were unable to open our Eustachian 

 tubes by merely swallowing, and were compelled to resort to a forced 

 expiratory effort with mouth and nose shut, the latter being held tight by 

 the finger and thumb. 



To one of us (L. H.) who had not practised beforehand the opening of his 

 Eustachian tubes, the first stance was most disturbing. The sensation of 

 increasing deafness and discomfort, more than discomfort, in the ears, with 

 no obvious cause, and the inability to gain relief by the recognised method 

 of swallowing, produced a feeling of mental distress which led to his 

 signalling to terminate the experiment. Once having learned the method 

 of opening his tubes, no such trouble resulted on subsequent occasions. 



As to whether one possesses any real sense of the amount of pressure, 

 the answer must be in the negative. V. Schrotter and his co-workers (11), 

 who made observations in caissons sunk in the Danube at from + - 5 to + 2'65 

 atmospheres, say that: " Bleibt nun der Druck stationar, verweilt die 

 Person auf langere Zeit unter einem bestimmten Drucke, so hort mehr oder 

 minder rasch, oft mit einem Schlage, jegliche unangenehme Sensation im 

 VOL. LXXVII. — B, 2 K 



