738 CHEMISTR Y OF RESPIRA TION. 



It is impossible to discuss here the different theories l brought forward to 

 explain the symptoms, but it appears that the most probable explanation is 

 that given by Bucquoy, 2 who maintains that the sudden fall in pressure sets 

 free the excess of gases dissolved in the blood during the exposure to the 

 compressed air of the caisson. These particles of gas in some of the small 

 blood vessels would cause embolism, and this would especially affect the nervous 

 system. Great support is given to this theory by the fact that workmen rarely 

 suffer when the change from the compressed air to the open air takes place 

 gradually by a slow fall in pressure, and that the most effective treatment for 

 the more serious symptoms is the subjection of the patient to compressed air. 

 This treatment 3 has been carried out in cases occurring among the workmen 

 employed in the construction of the Blackwall Tunnel under the Thames. 



In experiments upon animals, Paul Bert 4 found that the production 

 of carbon dioxide was diminished both when the animal was exposed 

 to a high or to a low atmospheric pressure. Lowy, however, observed 

 no alteration in the respiratory exchange of man, until the pressure of 

 the air fell below 300 mm. There was then an increase in the discharge 

 of carbon dioxide, but no corresponding increase in the intake of 

 oxygen. 5 



A gradual fall in the atmospheric pressure acts upon animals only 

 by decreasing the tension of the oxygen in the air, for, if the percentage 

 of oxygen be raised, a lower pressure can be borne. In air, discomfort 

 is felt when the pressure is reduced to half an atmosphere, and the 

 symptoms become violent with a pressure of 250 mm. ; convulsions, 

 insensibility, and death supervene. The limit of pressure appears to be 

 about 200 mm. Such are the results obtained by Paul Bert 6 during 

 experiments upon animals, and they agree with those observed upon man 

 during balloon ascents. Thus during the ascent of the Zenith 7 to a 

 height of 8600 metres, Sivel and Croce-Spinelli died, Tissandier became 

 unconscious, but recovered during the descent ; the pressure at that 

 height would correspond to 260 mm., and the tension of oxygen to 52 

 mm. According to Paul Bert's observations, the oxygen in the arterial 

 blood would be reduced to 10 volumes per cent. 



Many theories have been put forward to explain the symptoms of 

 " mountain sickness," but the true one appears to be that of Jourdanet, who 

 maintains that it is due to a condition of anoxyhsemia, a want of sufficient 

 oxygen in the blood. 8 In these cases the absorption of oxygen by the blood 

 would, at the low pressure of the atmosphere, be insufficient for the needs of the 

 tissues of a man or animal engaged in the exertion of climbing. It has been 

 objected 9 that this explanation is incorrect, because there appeared to be no 

 decrease in the amount of oxygen in the blood of dogs, which were subjected 

 by Frankel and Geppert to a reduced pressure, equal to that of an altitude of 



1 For further details, see Paul Bert's work, loc. cit., p. 520. 



2 " De 1'air comprimey' 1861. 3 Snell, loc. cit. 



4 Loc. cit., pp. 727, 805. 



5 For observations upon the effect of reduced atmospheric pressure on respiration, see 

 G. v. Liebig, Milnchen. med. Wchnschr., 1891, Bd. xxxviii. S. 437 ; Lowy, Arch. f. 

 Physiol., Leipzig, 1892, S. 545; Speck, Ztschr. /. klin. Med., Berlin, Bd. xii. S. 447. 



6 " La pression barome'trique," Paris, 1878, p. 735. 



7 Paul Bert, loc. cit., p. 1061 ; Tissandier, Nature, Paris, 1875, p. 337. 



8 A full discussion will be found in Paul Bert's work, loc. cit., p. 327. See also Clifford 

 Allbutt, "System of Medicine," London, 1897, vol. iii. p. 456. For the effects of high 

 altitudes upon the number of coloured blood corpuscles, see article on " Blood," p. 150. 



9 Grawitz, Berl. klin. Wchnschr., 1895, S. 713 and 740. 



