372 Mr. Leonard Hill [May 25, 



shown that animals, whose haemoglobin is satnrated with CO, can live in 

 2 atm. of pnre oxygen. So men with blood one third satnrated with 

 CO wonld be nnaffected in § atm. of oxygen, i.e. about 3 atm. of air, but 

 would become affected on decompression. If during and after decom- 

 pression the 0-2 supply is diminished by CO, and the heart enfeebled 

 thereby, less N2 will be given off, and the men may be affected both 

 by want of O2 and by N2 bubbles. The immediate success of recom- 

 pression, which E. Moir has had in recent cases at the Xew York 

 tunnels, suggests to me that CO may contribute to the numerous 

 accidents there, especially as, Mr. Moir tells me, 20 minutes are allowed 

 for decompression. He says that the men who use the diving-bells 

 at the Dover works are free from illness, in contrast to caisson workers 

 working at the same pressure. Here again the purity of the air from 

 CO is possibly one of the causes of the Dover immunity. 



The excessive heat and saturation of the air with moisture of 

 caisson works induces fatigue. The heat-regulating mechanism, 

 the heart and respiration, is sorely tried in keeping the body tem- 

 perature normal, while a man is doing heavy work at 80° F., and in 

 air completely saturated. The loss of sweat is enormous, but this by 

 drying the muscles may be of advantage by lessening the total 

 volume of body water and so of absorbed nitrogen. 



Any cause, then, which depresses the vigour of the workman in- 

 creases his risk from decompression. Hence the beneficial effects of 

 short shifts and ample ventilation. 



The men chosen for high-pressure work should be young, spare, 

 and wiry, and in perfect health. The man of spare habit has less 

 water in his body to take up N2. The man with powerful heart and 

 ample respiration can get rid of the dissolved N2 most readily. Some 

 men are more fitted than others, as experience shows, but no im- 

 munity to caisson illness can be estabhshed by habitual work in 

 compressed air. 



The experimental results obtained by rapid decompression have 

 unfortunately been amply confirmed on man by the results of ex- 

 plosion of caissons, or the air pipes of divers, on more than one 

 occasion. I recall the case of three workers who were sinking a well 

 in a brewery and working at +2*5 atm., when the air pipe burst. 

 The men were found dead. On dissection, bubbles of gas were visible 

 in all parts of the connective tissues and ])lood vessels. 



The post-mortem examination of fatal cases of caisson and divers' 

 paralysis are now fairly numerous (v. Leyden, Van Rensselaer, 

 Kikiforoff, Sharpless, v. Schrotter, etc.). They sliow lesions in the 

 S])inal cord, areas of degeneration and actual destruction brought 

 aljout by bul)bles here or there blocking capillaries and cutting off 

 the blood supply. The figures of such lesions shown on the 

 screen make evident the terrible risks run by compressed air workers. 



