CA KB ON DIOXIDE. 7 3 9 
I 
1G,000 feet. This may be so during rest, but it is probable that, on exertion, 
the slower rate of absorption would lead to a deficiencj in oxygen ; the organism 
accommodates, not for a condition of rest, but for exertion also ; it has a reserve 
store of energy. Thus, a man with marked anaemia, when he is at rest, absorbs 
as much oxygen ami produces as much carbon dioxide as a healthy man at 
rest, but, directly marked exertion is necessary, the anaemic subject becomes 
breathless; he has no reserve upon which to draw during the greatly aug- 
mented metabolism which accompanies muscular work. 
Nitrogen. — This gas appears to be quite inactive, and an animal 
confined in it dies from want of oxygen. The same seems to be true 
for argon. Nitrogen containing 5 per cent, oxygen was found by Sir 
George Johnson l to produce satisfactory anaesthesia in man within a 
minute ; this result is also to be attributed to want of oxygen. 
The question of the absorption or discharge of nitrogen by the lungs 
has been discussed in another part of this work. 
Hydrogen. — Numerous experiments have been made upon the 
effects of respiring hydrogen, and the general conclusion is that it 
produces no specific effect, but acts only by the exclusion of oxygen. 2 
Lavoisier and Seguin found that guinea-pigs respired in a normal 
manner in a mixture of equal parts of oxygen and hydrogen, and similar 
results were obtained upon dogs, rabbits, and frogs by Eegnault and 
Eeiset. Many cold-blooded animals can live for several hours in pure 
hydrogen. 3 
Carbon dioxide. — This gas in an undiluted state is irrespirable on 
account of the spasm of the glottis which it occasions, 4 but when suffi- 
ciently diluted with air or oxygen it can be respired, and produces head- 
ache, slight giddiness, drowsiness, and hyperpncea. Some of the earliest 
experiments with this gas were made by Priestley, 5 who found that cats 
died from suffocation when placed in carbon dioxide, and butterflies when 
held over the fermenting liquor in a brewery became motionless in a few 
minutes, but revived on being brought into the fresh air. Since that 
time numerous experiments have been made by different observers, 6 
especially by Paul Bert, whose results will be mentioned later. Brown- 
Srquard and d'Arsonval 7 state that they were able to breathe air 
containing 20 per cent, of pure carbon dioxide for two hours without 
any marked distress, but it is probable that there was some error in this 
observation, for Haldane and Lorrain Smith 8 found that when they 
breathed air containing 18 - 6 per cent, of this gas the following effects 
were produced within a minute or two — hyperpncea, distress, flushing, 
cyanosis, and mental confusion. Haldane 9 has further investigated this 
gas in connection with the suffocative gas found in w r ells and the 
" black-damp " of mines. 
1 Lancet, London, 1891, vol. i. 
- Scheele, " Ou Air and Fire," trans, by Forster, London, 1780, p. 160; Fontana, 
Phil. Trans., London, 1779, vol. lxix. p. 337 ; Jour a. de phys., Paris, tome xv. p. 99 ; 
Pilatre de Eozier, ibid., tome xxviii. p. 42o ; Lavoisier, Hist. Acad. roy. d. sc, Paris, 1789, 
p. 574 ; H. Davy, ' : Researches," p. 465 ; Allan and Pepys, Phil. Trans., London, 1809, 
p. 421. 
8 Spallanzani, Edwards, Johannes Miiller. See this article, p. 781. 
4 Pilatre de Rozier, Jowrn. de phys., Paris, tome xxviii. p. 422. 
5 Phil. Trans., London, 1772, vol. lxii. p. 147. 
6 For references, see Benedicenti, Arch. f. Physiol., Leipzig, 1896, S. 408. 
7 Compt. rend. Acad. d. sc, Paris, 1889, 11th Feb. 
8 Journ. Path, and Bacterid., Edin. and London, 1892, vol. i. p. 175. 
9 Trans. Fed. Inst, of Mining Engineers, 1895, vol. viii. p. 549. "The Causes of Death 
in Colliery Explosions," Government Blue Book, 1896. 
