742 CHEMISTR V OF RESPIRA TION. 
that the "noxious vapours" produced by repeatedly breathing the same 
air could he removed by potash, and the air rendered fit for respira- 
tion. A few years later, Black 1 showed that the " noxious vapours " 
were carbon dioxide. 
The importance of the several factors mentioned above has been differ- 
ently estimated by various observers. 2 Brown-Secpaard and d'Arsonval 3 
concluded that volatile poisons were given off from the lungs of healthy 
men and animals, for they found that the condensed vapour of breath 
caused death when injected into rabbits; that rabbits made to breathe 
air vitiated by the respiration of other rabbits until the carbon dioxide 
was 2 to 6 per cent., died, unless the supposed volatile poisons were 
removed by previously passing the air over pumice soaked in sulphuric 
acid ; that no bad effects were produced when men breathed for an 
hour or two air containing 20 per cent, of pure carbon dioxide. 
The experiment of injecting the condensed vapour of breath has been 
repeated by Dastre and Love, 4 Hoffmann- Wellenhof, 5 Lipari and Crisa- 
fulli, 6 and Lehmann and Jessen, 7 but the results were negative. 
Bichardson 8 maintained that breathed air was poisonous, even though 
all the carbon dioxide and other impurities had been removed ; the cause 
he considered to be " devitalised oxygen," whatever that term may mean. 
Jackson 9 thought that carbon monoxide was the poison. From experi- 
ments performed upon himself, Angus Smith 10 concluded that air vitiated 
by respiration until it contained 1 per cent, carbon dioxide, produced 
distinct feelings of discomfort. 
Experiments, however, performed by Hermans u have shown that 
no volatile poisons are given off by respiration, and more recently 
Haldane and Lorrain Smith, 12 in an investigation of the subject, both 
as regards animals and men, have confirmed and extended Hermans' 
work. The following are the chief conclusions given by Haldane and 
Lorrain Smith : — 
" 1. The immediate dangers from breathing air highly vitiated by 
respiration arise entirely from the excess of carbon dioxide and 
deficiency of oxygen, and not from any special poison. 
"2. The hyperpncea is due to excess of carbon dioxide, and is not 
appreciably affected by the corresponding deficiency of oxygen. The 
hyperpncea begins to appear when the carbon dioxide rises to from 
3 to 4 per cent. At about 10 per cent, there is extreme distress. 
"3. Excess of carbon dioxide is likewise the cause, or at least one 
cause, of the frontal headache produced by highly vitiated air. 
" 4. Hyperpnoea from defect of oxygen begins to be appreciable when 
the oxygen in the air breathed has fallen to a point which seems to 
1 "Lectures on Chemistry," ed. Robison, Edinburgh, 1S03. 
2 See Merkel, A rch. f. Hyg., Miinchen u. Leipzig, 1S92, Bd. xv. S. 1, where further 
references are given. 
3 Compt. rend. Acad, d. sc, Paris, 1888, tome cvi. pp. 106, 165 ; Oompt. rend. Soc. de 
bioh, Paris, 1887, p. 814 ; 1S88, pp. 33, 90, 99, 151. 
4 Hid., 1888, pp. 43 and 91. 
5 Wien. klin. Wchnschr., December 13, 1888. 
15 Bull. gin. de therap. etc., Paris, 1889, No. 46, p. 524. 
7 Arch./. Hyg., Miinchen u. Leipzig, 1S90, Bd. x. S. 367. 
8 Brit. Med. Journ., London, 1860, vol. ii. ; Chem. News, London, vol. lv. p. 253. 
9 "Proc. Physiol. Soc," December, 18S7, in Journ. Physiol., Cambridge and London, 
vol. ix. 
10 "Air and Rain," p. 130. 
11 Arch./. Hyg., Miinchen u. Leipzig, 18S3, Bd. i. 
12 Journ. Path, and Bacterial., Edin. and London, 1892, vol. i. p. 175. 
