October 26, 191 1] 



NATURE 



569 



•of CO, given off is trebled or quadrupled, and during hard 

 work it may be increased sixfold. The ventilation of the 

 lung is increased pari passu so as to keep the percentage 

 of C0 2 in the lung normal. 



If the pressure of CO, in the inspired air is increased, 

 the breathing is deepened so as to keep normal the CO, 

 percentage in the lung. If the inspired air contain 3 per 

 cent. CO., the volume breathed is about doubled, and 

 moderate work in such air causes as much panting as 

 hard work in pure air. 



When the atmospheric pressure is altered it is not the 

 percentage, but the absolute pressure of C0 2 which controls 

 the breathing. Thus the percentage found in Greenwood's 

 lungs was 5-4 at one atmosphere, 2-7 at two atmospheres, 

 09 at six atmospheres, and the partial pressure of CO, — 

 i.e. the percentage multiplied by the pressure in atmo- 

 spheres—in each case was 5-4 per cent, of an atmosphere. 

 This holds good also down to about two-thirds of an 

 atmosphere in analyses taken at high altitudes. At lower 

 atmospheric pressures than this oxygen want comes in, 

 with the production of lactic acid in the tissues and blood 

 as a disturbing factor. It is clear, then, that the effect of 

 a given percentage of CO, in the diver's helmet varies 

 with the depth. If air containing 5 per cent. CO, pro- 

 duces great panting at one atmosphere, air containing 

 S/7'4 = o-68 per cent, will produce the same degree of pant- 

 ing at 35 fathoms (7-4 atmospheres). It follows from this 

 that whatever the pressure a diver is under, he requires 

 the same volume of air measured at that pressure to ensure 

 the ventilation of his helmet. At two atmospheres the 

 ventilation must be doubled, at three atmospheres trebled, 

 at six atmospheres increased sixfold. Under the old con- 

 ditions of working, often with leaky pumps and tired men 

 to pump, the ventilation has been actually less, not six 

 times greater, as it ought to be, at a depth of 165 feet. 



With a pressure of 2 per cent, of C0 2 in the inspired 

 air the pulmonary ventilation is increased about 50 per 

 cent., with 3 per cent, about 100 per cent., with 4 per 

 cent, about 200 per cent., with 5 per cent, about 300 per 

 cent., and with 6 per cent, about 500 per cent. If the 

 •diver is working hard the extra production of CO, will 

 make him pant, and this, coupled with the effect of the 

 excess in the helmet, which often reaches 3 to 4 per cent., 

 makes breathing distressing and the feeling of oppression 

 intense. Thus at a depth of 139 feet with a CO, pressure 

 of 4-28 per cent, of an atmosphere, Lieut. Damant was 

 unable to continue for more than eight minutes the exer- 

 tion of lifting a weight of 56 lb. about 9 feet per minute. 

 The Admiralty Committee found that the divers could 

 continue work for long periods at depths of even 210 feet 

 so long as the CO, pressure was kept below 3 per cent, 

 of an atmosphere. 



To keep the CO, down to this level a diver ought to 

 have at least 1-5 cubic feet of air per minute when work- 

 ing, and he must have this volume of air pass through 

 the helmet at whatever pressure he be at. Each cylinder 

 of the regulation service pump ought to yield one-tenth 

 cubic feet per revolution. Assuming an unavoidable leak- 

 age of the pumps of 10 per cent, at 100 feet and 24 per 

 cent, at 200 feet, the Admiralty Committee ordered for 

 33 feet (depth) one cylinder, thirty revolutions per minute, 

 and two men per spell, the work being estimated at 

 4440 foot-lb. per minute : while for 165 feet depth four 

 cylinders, twenty-seven revolutions, and twelve men are 

 required, the work being 34,000 foot-lb. per minute : for 

 iqR feet (depthl six cylinders, twentv-three revolutions, 

 eighteen men, the work being 43,000 foot-lb. per minute. 

 Provision ought to be made to give a third more than this 

 supply if the diver gets into difficulties. 



At 210 feet thirtv-six men were working very hard in 

 alternate five-minute spells of rest and work, and were 

 scarcely able to keep up the proper air supplv. Long 

 handles were supplied to allow three men on each side of 

 the pump. 



To avoid this excessive labour. R. H. D; vis (of Siebe. 

 Gorman and Co.) and I have added to the diving dres« 

 this metal box. containing trays of caustic soda. A mouth- 

 piece is placed within the helmet, and a tube leads from 

 this through the soda-box and back to the helmet. The 

 diver when oppressed in the slightest degree can take hold 

 of the mouthpiece with his lips and breathe through the 



NO. 2 igi, VOL. 87] 



caustic soda, and so lessen the concentration of CO a . 

 There is no risk of his suffering from want of oxygen so 

 long as the pumps give him a moderate supply of air. 

 This device ought to save a great deal of hard pumping 

 work. 



The Self-contained Diving Dress. 

 We have also contrived a self-contained diving dress 

 fitted with cylinders containing compressed air enriched 

 with oxygen (to 50 per cent.), and a caustic-soda chamber. 

 The oxygen supply is delivered to the helmet by a re- 

 ducing valve in constant supply (5 litres per minute), and 

 the force of the oxygen stream is used, by means of an 

 injector, to suck the air in the helmet through the caustic- 

 soda chamber. No life-line or air-pipe is carried, only a 

 light telephone cable, and this makes the dress suitable for 

 exploration of flooded mines, tunnels, ships, &c, through 

 which the heavy pipes and lines cannot be dragged. Air 

 containing 50 per cent, oxygen is used in place of oxygen 

 (Haldane), so that there is no risk of oxygen poisoning if 

 used for an hour at depths of 70 to 80 feet, or even 

 100 feet, for half an hour. 



Compressed-air Illness. 



In all the great compressed-air works from first to last 

 the men have suffered from illness and loss of life. There 

 is no risk going into or staying in the caisson, as Pol and 

 Watelle (1854) said, " On 'ne paie qui'en sortant." Out 

 of sixty-four workers observed by them forty-seven re- 

 mained well, fourteen had slight illnesses, sixteen more or 

 less severe, two died. An absolute pressure of 4i atmo- 

 spheres was reached. The men worked two shifts per diem 

 of four hours each, and were decompressed in thirty 

 minutes. At the St. Louis Bridge works, out of 352 

 workers there were 119 cases, fifty-six of paralysis, and 

 fourteen deaths. The absolute pressure reached 4! atmo- 

 spheres. 



At the Nussdorf works 320 cases among 675 workers, and 

 two deaths ; the absolute pressure reached was 3J atmo- 

 spheres. 



In the East River tunnels (New York), under well- 

 regulated conditions, the percentage of illness was o-66, 

 of death 0-0035 m 557> 00 ° man-shifts, with a decompression 

 rate of fifteen minutes from an absolute pressure of three 

 atmospheres. Of the 320 cases at Nussdorf, v. Schrotter 

 observed sixty-eight cases of ear trouble, 105 of pain in 

 the muscles, sixty of pains in the joints, ten of girdle 

 pains, seventeen of partial paralysis, twenty-six of 

 paralysis of the lower half of the body, fourteen of vertigo 

 and noises in the ear, two of sudden deafness, one of loss 

 of speech, thirteen of asphyxial phenomena. Out of 3692 

 cases at the East River tunnels o'bserved by Keays, 8878 

 per cent, were pains in joints and muscles, " bends," 

 1-26 per cent, pains and prostration, 2-16 per cent, nervous 

 symptoms, 5-33 per cent, vertigo, 1-62 per cent, dyspnoea 

 and oppression, chokes, 046 per cent, loss of conscious- 

 ness and collapse. There were twenty deaths. _ The trouble 

 in the ear, which occurs during compression, is due to the 

 inequality of air pressure on either side of the drum of the 

 ear. It is relieved at once by opening the Eustachian tubes 

 by swallowing, or by a forced expiration with the nose and 

 mouth held shut. None of the other manifold symptoms 

 come on while the men are under pressure. Mules were 

 kept for a year in the Hudson Tunnel at three atmospheres 

 absolute, and were healthy enough to kick and bite at all 

 comers (E. W. Moir). The illness comes in after decom- 

 pression, usuallv within a few minutes to half an hour, 

 sometimes even later. 



The Cause of the Illness. 



The cause of the illness — so striking in its protean 

 nature — was made clear by Paul Bert (1S79), who showed 

 bv experiments on animals (1) that nitrogen gas is dis- 

 solved by the blood and tissue fluids in proportion to the 

 pressure of the air (Dalton's law); (2) that the dissolved 

 gas bubbles off and effervesces in the blood when an animal 

 01 man is decompressed too rapidly; the bubbles, by 

 blocking up the capillaries and cutting off the blood supply 

 here or there, produce the symptoms ; (3) that during ex- 

 M eight or nine atmospheres there is no ill-effect 



