7 o 4 CHEMISTR Y OF RESPIRA TION. 
The respiration of fishes. — The necessity of air for the life of fishes 
was proved by Boyle * during his experiments with the air-pump. He states 
that " there is wont to lurk in water many little parcels of interspersed air, 
whereof it seems not impossible that fishes may make some use, either by 
separating it when they strain the matter through their gills, or by some other 
way." Mayow 2 (1674) appears to have been the first to understand and to 
correctly describe how fish breathed by taking up nitro-aerial gas (oxygen) 
from the water by means of the blood flowing through their gills ; and Ber- 
nouilli 3 in 1690 demonstrated that fish could not live in cold water from 
which the air had been expelled by boiling. 
The methods employed and quantitative results obtained by different 
observers, who have studied the respiration of fishes and other animals living 
in water, have already been described. A few additional facts, however, 
must be mentioned. Humboldt and Provencal ' state that nitrogen was in 
some cases absorbed, but Avhen the water was impregnated with oxygen and 
hydrogen none of the latter gas was taken up by the fishes ; a certain amount 
of cutaneous respiration also occurs, and fishes can breathe in the air as long as 
their gills are kept moist with water. The respiration of fishes living in the 
sea is facilitated by the absence of any free carbon dioxide in the water, for 
any carbon dioxide formed is at once fixed by the excess of alkaline base 
present in the water. 5 
In connection with the respiration of fishes, the svoimming-bladder must be 
considered, for this organ is one which can secrete gases and in some cases 
store up almost pure oxygen. 
Biot 6 found that the percentage of oxygen increased with the depth from 
which the fish was taken ; the greatest percentage was 87. This was con- 
firmed by the observations of Delaroche, 7 who obtained 70 per cent, oxygen from 
the bladder of fishes drawn up from a greater depth than 50 metres (164 feet), 
and 29 per cent, from those taken at smaller depths. Erman, 8 Yauquelin, 9 
Configliachi, 10 and Delaroche n analysed the gas in the swimming-bladder of 
fresh-water fish, and found the percentage of oxygen generally less than that 
in the atmosphere, little or no carbon dioxide, but much nitrogen. The mean 
of analyses made by Humboldt and Provencal showed 7T parts of oxygen, 
5 "2 of carbon dioxide, and 87 "7 parts of nitrogen in 100 volumes of gas from 
the swimming-bladder of a carp, while the results obtained by F. Schultz I2 
varied between PI and 13*2 per cent, oxygen and P4 and 5"4 per cent, carbon 
dioxide. 
According to Humboldt and Provencal, the tench (Oyprinus tinea), in winch 
there is a duct communicating between the air-bladder and the mouth, does 
not take hydrogen into its bladder when the water in which it is confined is 
saturated with that gas. Moreau obtained similar negative results ; but more 
1 "Xew Experiments, Physico-Mechanical, touching the Spring of the Air," 1662; 
Phil. Trans., London, 1670, pp. 2011, 2035 ; "Works," Shaw's edition, vol. i. p. 109. 
2 "Traetatus quinque," Oxon., 1674, vol. i. ch. xv. p. 259. 
3 " Dissertatio do eti'ervescentia et fermentatione nova hypothesi fundata," ch. xiv. 
Basilite, 1690. 
4 Mem. de la Soc. dc phys. et de chim. d' Armed, Paris, 1809, tome ii. p. 359 ; Journ. 
f. Chem. u. Phys., Niirnberg, 1811, Bd. i. S. 86. 
5 Dittmar, Proc. Phil. Soc. Glasgoiv, vol. xvi. p. 61 ; M'Kendrick, Nature, London, 
1888, Aug. 16 ; Brit. Med. Journ., London, 1S88, vol. ii. p. 331 ; Petersen, Scottish 
Geograph. Mag., Edinburgh, 1895, June, p. 294. 
,; Mtm. de la Soc. dc i^hys. et dc chim. d'Arcueil, Paris, 1807, tome i. p. 252 ; Ann. d. 
Phys. u. Chem.. Leipzig. Bd. xxvi. S. 454. 
7 Journ. f. Chem. a. Phys., Niirnberg, 1811, Bd. i. S. 122. 
8 Ann. d. Phys. u. Chem., Leipzig, 1808, Bd. xxx. S. 113. 
9 Yauquelin. quoted from Erman, reference 8. 
10 Joura. f. i 'In m. u. Phys., Niirnberg, 1S11, Bd. i. S. 137. 
11 Ibid., S. 164. 
12 Arch. f. d. nes. Physiol., Bonn, 1872, Bd. v. S. 48. 
