CARBON DIOXIDE. 739 



16,000 feet. This may be so during rest, but it is probable that, on exertion, 

 the slower rate of absorption would lead to a deficiency 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 and 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 x 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 

 Reiset. 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- 

 Sequard 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 hyperpnoea, distress, flushing, 

 cyanosis, and mental confusion. Haldane 9 has further investigated this 

 gas in connection with the suffocative gas found in wells and the 

 " black-damp " of mines. 



1 Lancet, London, 1891, vol. i. 



2 Scheele, "On Air and Fire," trans, by Forster, London, 1780, p. 160; Fontana, 

 Phil. Trans., London, 1779, vol. Ixix. p. 337 ; Journ. de phys., Paris, tome xv. p. 99 ; 

 Pilatre de Rozier, ibid., tome xxviii. p. 425 ; Lavoisier, Hist. Acad. roy. d. sc., Paris, 1789, 

 p. 574; H. Davy, "Researches," p. 465 ; Allan and Pepys, Phil. Trans., London, 1809, 

 p. 421. 



3 Spallanzani, Edwards, Johannes Miiller. See this article, p. 781. 



4 Pilatre de Rozier, Journ. dephy*., Paris, tome xxviii. p. 422. 



5 Phil. Trans., London, 1772, vol. Ixii. p. 147. 



6 For references, see Benedicenti, Arch. f. PhysioL, Leipzig, 1896, S. 408. 



7 Compt. rend. Acad. d. sc., Paris, 1889, llth Feb. 



8 Journ. Path, and Bacterial., 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. 



