1006.] on Compressed Air and its Physiological Effects, 367 



V. Schrotter, at Nussdorf, observed 68 cases of ear trouble, 105 of pain 

 in the muscles, 60 of pain in the joints, 10 of i^irdle pains, 17 of 

 partial paralysis, 26 of paralysis of the lower half of the body, 14 

 of vertigo and noises in tlie ears, 2 of sudden deafness, 1 of loss of 

 speech, 13 of asphyxia] phenomena. 



Xone of the symptoms, with the exception of some slight ear 

 trouble, ever occur while the men are under pressure. Mules lived 

 about a year in the Hudson tunnel, and were healthy enough to kick 

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

 pression, usually within a few minutes to half an hour, sometimes 

 even later. 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 reheved at once by opening the Eustachian tubes by 

 swallowing, or, if this is not enough, by a forced expiratory effort 

 with the nose and mouth shut. 



Many and conflicting were the theories of compressed air illness, 

 and in the directions given to avoid it. Some medical men (Pol and 

 Watelle) recommended slow, and others, like Foley, rapid decom- 

 pression, xlll was made clear by a remarkable series of experiments 

 carried out by Paul Bert on animals between 1870-1880. By these 

 experiments he not only proved the cause, but found the means of 

 prevention. 



Bert showed that nitrogen gas is dissolved by the blood and body 

 fluids in proportion to the pressure of the air, and that the gas 

 bubbles off in the blood, when an animal or man is rapidly de- 

 compressed. The bubbles may block up the capillaries in one or 

 other part of the body, and by cutting off the part from blood supply, 

 produce one or other of the symptoms mentioned above. The illness 

 is prevented by making the period of " decompression " sufficiently 

 slow, i.e. by allowing time for the dissolved nitrogen to escape from 

 the lungs.* 



Bert's experimental results have been confirmed and extended by 

 B. Blanchard and P. Regnard, Catsaras, Philippon, Layet and 

 Hersent, H. v. Schrotter, R. Haller and W. Mager, and by myself 

 and my colleagues, J. J. P. Macleod, C. Ham, and M. Greenwood. 

 The whole matter in consequence is placed on a sure footing. 



Exposed to 1 atm. at body temperature, blood dissolves just about 

 1 per cent. Xg, to 2 atm, 2 per cent., to 3 atm. 3 per cent., and so on. 

 The tissue fluids take up the dissolved gas from the blood, and with 



* Boyle, 200 years previously, had shown that gas bubbles appeared in the 

 humours of the eye of a viper, when submitted to a rapid evacuation under 

 the air pump. Hoppe Seyler, repeating Boyle's experiment, found gas bubbles 

 collected in the veins of a raammal, which was very rapidly lowered to 70- 

 80 mm. Hg. ; the bubbles caused convulsions which might be stayed by the 

 introduction of hydrogen at atm. pressure. The asphyxial convulsions which 

 arose from want of oxygen occurred 2 minutes later. Rapid evacuation to 

 75 mm. Hg. in an atm. of oxygen caused convulsions, no less, owing to the 

 setting free of nitrogen bubbles. 



