7 38 CHEMISTR Y OF RESPIRA TION. 
It is impossible to discuss here the different theories 1 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 Croee-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 anoxyhamiia, 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 iff an altitude of 
1 For further details, see Paul Bert's work, loc. cii., p. 520. 
2 " De Fair com prime," 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, Miinchcn. mccl. Wchnschr., 1S91, Bd. xxxviii. S. 437 : Lowy, Arch. /. 
Physiol., Leipzig, 1892, S. 545: Speck, Ztschr. f. klin. Med., Berlin, Bd. xii. S. 447. 
6 "La pression barometrique," Paris, 1878, p. 73">. 
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. 
