7 o 4 CHEMISTRY OF RESPIRATION, 



The respiration of fishes. The necessity of air for the life of fishes 

 was proved by Boyle l 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 4 state that nitrogen was in 

 some cases absorbed, but when 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 swimming-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 Vauquelin, 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 Prove^al showed 7'1 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 12 

 varied between 1*1 and 13*2 per cent, oxygen and 1'4 and 5*4 per cent, carbon 

 dioxide. 



According to Humboldt and Provencal, the tench (Cyprinus tinea], in which 

 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 "New 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 "Tractatus quinque," Oxon., 1674, vol. i. ch. xv. p. 259. 



3 "Dissertatio de effervescentia et fermentatione nova hypothesi fundata," ch. xiv. 

 Basilite, 1690. 



4 Mm. de la Soc. de phya. et de chim. d'Arcueil, Paris, 1809, tome ii. p. 359 ; Journ. 

 f. Chem. u. Phys., Nurnberg, 1811, Bd. i. S. 86. 



5 Dittmar, Proc. Phil. Soc. Glasgow, vol. xvi. p. 61 ; M'Kendrick, Nature, London, 

 1888, Aug. 16 ; Brit. Med. Journ., London, 1888, vol. ii. p. 331 ; Petersen, Scottish 

 Gcograph. Mag., Edinburgh, 1895, June, p. 294. 



6 Mem. de la Soc. de phys. et de chim. d'Arcueil, Paris, 1807, tome i. p. 252 ; Ann. d. 

 Phys. u. Chem., Leipzig. Bd. xxvi. S. 454. 



7 Journ. f. Chem. u. 'Phys., Nurnberg, 1811, Bd. i. S. 122. 



8 Ann. d. Phys. u. Chem., Leipzig, 1808, Bd. xxx. S. 113. 



9 Vauquelin, quoted from Erman, reference 8. 



10 Journ. f. Chem. u. Phys., Niirnberg, 1811, Bd. i. S. 137. 



11 Ibid., S. 164. 



12 Arch.f. d. ges. Physiol., Bonn, 1872, Bd. v. S. 48. 



