EVENING DISCOUKSES. 639 



Compressed-air Illness. 



In all me 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 qu'en sortant.' Out of 64 workers 

 observed by them, 47 remained well, 14 had slight illnesses, 16 more or less 

 severe, 2 died. An absolute pressure of 4^ atmospheres was reached. The men 

 worked two shifts per diem of 4 hours each, and were decompressed in 30 minutes. 

 At the St. Louis Bridge works, out of 352 workers there were 119 cases, 56 of 

 paralysis, and 14 deaths. The absolute pressure reached 4j atmospheres. 



At the Nussdorf works 320 cases among 675 workers and 2 deaths, the absolute 

 pressure reached was 3g atmospheres. 



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

 percentage of illness was 066, of death 0'0O35 in 557,000 man-shifts, with a 

 decompression rate of 15 minutes from an absolute pressure of 3 atmospheres. 

 Of the 320 cases at Nussdorf, Von Schrotter observed 68 cases of ear trouble, 105 

 of pain in the muscles, 60 of pains in the joints, 10 of girdle pains, 17 of partial 

 paralysis, 26 of paralysis of the lower half of the body, 14 of vertigo and noises 

 in the ear, 2 of sudden deafness, 1 of loss of speech, 13 of asphyxial phenomena. 

 Out of 3,692 cases at the East River tunnels observed by Keays 88-78 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 consciousness and collapse. There 

 were 20 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 comes on while the men are under pressure. Mules were kept for a year 

 in the Hudson Tunnel at 3. atmospheres absolute, and were healthy enough to 

 kick and bite at all comers (E. W. Moir). The illness comes on after decom- 

 pression, usually 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 (1879), who showed by experiments on animals (1) that nitrogen gas 

 is dissolved 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 or man is decompressed too rapidly — the bubbles by 

 blocking up the capillaries, and cutting off the blood supply here or there, pro- 

 duce the symptoms ; (3) that during exposure to 8 or 9 atmospheres there is no 

 ill-effect until the partial pressure of oxygen dissolved in the blood reaches such 

 a point that it acts as a tissue poison ; (4) that the illness, which occurs on decom- 

 pression, is prevented by making the period of decompression sufficiently slow, by 

 allowing time for the dissolved nitrogen to escape from the lungs. Looking 

 through the works of Robert Boyle, I found that, after the invention of his air- 

 pump, he ' had a mind to observe whether when the air from time to time was 

 drawn away, there would not appear some hidden swelling, greater or less, of the 

 body of the animal by the spring and expansion of some air (or aerial matter) 

 included in the thorax or the abdomen.' He recorded that a viper's body and 

 neck grew prodigiously tumid ; that a bubble of air appeared in the aqueous 

 humour of a viper's eye ; that the heart of an eel grew very tumid and sent forth 

 little bubbles ; that blood boiled ' over the pot ' until the blood occupied only one- 

 quarter of the volume of the whole, so great was the expansion of the bubbles 

 given off from it. In the following surmise, concerning the death of animals 

 submitted to rarefaction, Boyle forestalls Bert. ' Another suspicion we should 

 have entertained concerning the death of animals — namely, that upon the sudden 

 removal of the wonted pressure of the ambient air, the warm blood of those 

 animals was brought to an effervescence or ebullition ; or at least so vehemently 

 expanded, as to disturb the circulation of the blood, and so disorder the whole 

 economy of the body.' 



Hoppe-Seyler (1857) demonstrated bubbles in the blood-vessels of animals 

 submitted to rarefaction. This was denied by Bert, but confirmed in the case of 

 a rabbit by Greenwood and myself. 



