NO. 2$ INFLUENCE OF ATMOSPHERE ON HEALTH 23 



cent; and with 6 per cent, about 500 per cent. With the last, pant- 

 ing- is severe ; while with 3 per cent it is unnoticed until muscular 

 work is done, when the panting is increased 100 per cent more than 

 usual. With more than 6 per cent the distress is very great, and 

 headache, flushing, and sweating occur. With mure than 10 per 

 cent there occurs loss of consciousness after a time, but no immediate 

 danger to life. Even exposure to 25 per cent may not kill an animal 

 within an hour or two. 



Such high concentrations, when sufficient 2 is supplied, poison 

 the heart and lower the blood-pressure (Hill and Flack). 



It is only when the higher concentrations of C0 2 are breathed, 

 such as 3 to 4 per cent of an atmosphere, that the respiration is 

 increased so that it is noticeable to the resting individual ; but per- 

 centages over 1 per cent diminish the power to do muscular work, 

 for the excess of C0 2 produced by the work adds its effect to that 

 of the excess in the air, and the difficulty of coordinating the breath- 

 ing to the work in hand is increased. Nevertheless, divers who 

 work in diving dress and men at work in compressed-air caissons 

 constantly do heavy and continuous labor in concentrations of C0 2 

 higher than 1 per cent of an atmosphere, and so long as the C0 2 

 is kept below 2 to 3 per cent they are capable of carrying out efficient 

 work. The excess of oxygen helps them. In the case of workers in 

 compressed air it is important to bear in mind that the effect of the 

 C0 2 on the breathing depends on the partial pressure and not on the 

 percentage of this gas in the air breathed. 1 Thus the volume of air 

 breathed was increased 2 to 2.5 times by inhaling 5 per cent C< ) 2 

 at 1 atmosphere, and to the same extent by inhaling 1.6 per cent at 

 3./ atmospheres. The partial pressure in the two cases was approxi- 

 mately the same. It follows from this that whatever the pressure a 

 diver is under he requires the same volume of air for ventilation, 

 measured at that pressure. Thus at 2 atmospheres (33 feet depth 

 of water) the air supply, measured at atmospheric pressure where 

 the pump is, must be doubled ; at 3 atmospheres, trebled ; and so on. 



In the boring of the St. Gothard tunnel the laborers carried out 

 the work in an atmosphere containing 0.3 to 0.96 per cent C0 2 . At 

 the altitude of the tunnel the partial pressure was considerably less, 

 but yet far above that set as the limit in factories. In the com- 

 pressed-air caisson at Nussdorf the CO. percentage varied from .04 

 to 0.5, and the partial pressure was about three times this amount, 

 that is, equivalent to 0.12 to 1.5 per cent at sea-level. 



1 Haldane and Priestley, Journ. of Physiol., Vol. 32, 1905. p. _>_'5, and Report 

 of Admiralty Committee on Deep-sc-a Diving, 1905. 



