RESPIRATION 339 



respiration, as is commonly the case in diving, carbon dioxide 

 also comes into consideration. The case of this gas may be con- 

 sidered first, though Paul Bert did not himself allude to it in 

 connection with work in compressed air, as he was not practically 

 familiar with diving. 



Owing to the difficulties frequently experienced by divers in 

 attempts to work at depths over about 12 fathoms a Committee, 

 including myself as the physiological member, was appointed by 

 the British Admiralty to investigate the whole subject of the 

 difficulties and dangers associated with deep diving.^ It appeared 

 that men who attempted to make any serious exertion when at 

 depths of over about 12 fathoms often became unconscious or 

 greatly exhausted. The symptoms pointed to excess of CO2, and, 

 on taking samples from the divers' helmets at about this depth, 

 we frequently found 2 or 3 per cent of COo. This occurred in spite 

 of an apparently abundant supply of air from the pumps, which 

 were working at a much faster rate than was sufficient to keep the 

 diver comfortable at a lesser depth. As explained in Chapter II, 

 the physiological effects or 3 per cent of CO2 at 1 1 fathoms, or a 

 total pressure of three atmospheres, is equal to that of 3 x 3 = 9 

 per cent at normal atmospheric pressure; so no wonder the divers 

 became unconscious. The pumps were often found to be leaking 

 badly through the piston rings, as many of them were old, and 

 no tests were then employed to detect this leakage. Apart from 

 this cause, however, the air supply was often insufficient. 



It is evident that in order to keep down the pressure of COg 

 in the air of the helmet to a proper limit, the amount of air as 

 measured at surface by the strokes of the pump must be increased 

 in proportion to the increase in the total atmospheric pressure in 

 the helmet. The diver at 3 atmospheres pressure, requires, there- 

 fore, three times as much air, and so on in proportion to the 

 pressure. When this was attended to, and the piston rings kept 

 tight, no discomfort whatsoever was experienced at a depth of 

 even 35 fathoms. With a full air supply, hard exertion is actually 

 easier to a diver at some depth than near surface, on account of 

 the higher oxygen pressure, as explained in Chapter IX. 



By far the most serious danger to divers and other workers in 

 compressed air is of a quite different character. From the earliest 

 days of diving and work in compressed air it had been observed 

 that soon after returning to atmospheric pressure the men fre- 



^ Report of the Admiralty Committee on Deep Water Diving, Pari. Paper, C. N., 



1549. 1907- 



