EVENING DISCOURSES. 645 



The quickest method of desaturating the body is to ' wash ' the nitrogen 

 out, by breathing oxygen for a few minutes before and during decompression. 

 The only question is the safety of this proceeding, for high concentrations of 

 oxygen act as a poison. 



Oxygen Poisoning. 



(1) All kinds of animals, worms, snails, flies, spiders, frogs, &c. are instantly 

 convulsed and killed by exposure to 50 atmospheres oxygen ; (2) The frog's 

 heart beats, nerve conducts and muscle contracts for some time in 50 atmo- 

 spheres oxygen, but there is evidence of progressive diminution in functional 

 power, the muscles behave like a fatigued muscle ; (3) Mice exposed to 10 atmo- 

 spheres oxygen are thrown into tetanic spasms, and on being decompressed 

 continue to be convulsed by a touch. Bubbles of oxygen are to be then found 

 in the central nervous system compressing the nerve cells. As the bubbles are 

 oxygen the cells do not die and the animals may recover, the oxygen being 

 absorbed by the tissues and the circulation re-established ; (4) + 3 atmospheres 

 oxygen convulsed animals in 30 to 60 minutes (Bert and Lorrain Smith), and 

 the poisonous effect, depending as it does on the partial pressure of oxygen in 

 the blood, comes on just as soon in larger animals as in small, e.g., cats, rats, 

 and mice ; (5) Fatal inflammation of the lung is produced by exposure to high 

 partial pressures of oxygen, e.g., after 25 hours' continuous exposure to +7 

 atmospheres of air = 170 per cent, atmosphere oxygen (Lorrain Smith). This 

 can be prevented by using nitrogen to dilute the air, and so lowering the partial 

 pressure of oxygen; (6) It is quite safe to breathe 1 atmosphere oxygen, or 

 5 atmospheres air, for 3 to 4 hours. The men who wear the Fleuss apparatus 

 for rescue work in mines have breathed it day after day for this period. I 

 have spent much time with Mr. R. H. Davis in perfecting this apparatus on 

 physiological lines, and so have studied particularly the effect of oxygen on man. 

 In very hard work there may be a deficiency of the oxygen supply in the body, 

 and then breathing oxygen helps the working power of the man. 



If the body is getting enough oxygen the breathing of it has no effect on the 

 metabolism. The man at rest cannot be fanned into a greater rate of activity 

 by breathing oxygen. Poisonous pressures of oxygen lower the metabolism and 

 diminish the carbonic acid output of animals. Martin Flack and I showed 

 that the breathing of oxygen just before a race may help an athlete, because 

 during his great effort he uses up oxygen quicker than his respiration and circu- 

 lation can provide it. A shortage of oxygen leads to the production of acid 

 products in the tissues and blood, which causes breathlessness and stiffness of 

 the muscles. 



Lactic acid appears in the urine after a short period of hard running 

 (Ruffel). Feldman and I have found that breathing oxygen by means of the 

 Fleuss dress during the run prevents the excretion or lessens the amount of 

 lactic acid excreted. Thus the pressure of oxygen helps the caisson worker to 

 do his work more easily. During decompression it is of no advantage to him 

 to have the pressure of oxygen lowered. 



Bornstein at the Elbe Tunnel works has breathed oxygen (90 to 95 per cent.) 

 for forty-eight minutes at a pressure of 3 atmospheres. Two other engineers 

 breathed it for thirty minutes. Bornstein freed himself from 'bends' by this 

 means. These periods are the outside limits of safety. Bornstein began to have 

 slight convulsive movements. 



For every atmosphere the body dissolves nitrogen to about 1 per cent, of 

 its mass, for a 70 kgm. man, say, 1,000 cc. per atmosphere. Von Schrotter calcu- 

 lates that oxygen plus exercise would turn out 1,000 cc. in five minutes, probably 

 more. 



Oxygen can be breathed economically by means of the Fleuss apparatus 

 which was used so effectively in the last great colliery disaster at Bolton. The 

 apparatus can be put on and oxygen breathed for ten minutes before and during 

 decompression. The breathing-bag must be washed out several times with a 

 current of oxygen, from the emergency valve provided, to accelerate the output 

 of nitrogen. 



J. F. Twort and I have investigated the effect of breathing oxygen on the 

 vol ume of nitrogen dissolved in the urine. Precautions were taken to collect 

 the urine without contact with the atmosphere. About three pints of water 



