138 CIRCULATING FLUIDS : 



and the number of the fishes. The ratios of the consumed 

 oxygen to the carbonic acid formed, -were as 1 to 'o7, "80, 'Ol, 

 •20, and '50, while the ratios of the consumed oxygen to the 

 consumed nitrogen were as 1 to •43, "87, "40, '19, '71, and "63. 

 The inequahty of these ratios indicates, as Berzelius remarks, 

 the varying power with which fishes act upon the air on dif- 

 ferent days, at different seasons, and possibly in different con- 

 ditions of health.^ 



The amount of 0x3' gen consumed by fishes is much less than 

 would be required for warm-blood animals of equal bulk,^ and 

 their temperatiu'e is verj^ little above that of the surrounding 

 medium. When breathing free atmospheric air, they do not 

 consume more oxygen than in then native element. 



Fishes absorb oxygen and exhale carbonic acid, not merely 

 with their gills but with the whole surface of their body, as 

 long as they are surrounded with water impregnated with at- 

 mospheric air. This fact was proved by Humboldt in the fol- 

 lowing manner. He passed a cork collar, covered with waxed 

 cloth, over the head of a fish, Avhich was then introduced into 

 a vessel filled with water, the vessel being closed by the cork 

 collar, which was so adjusted that the head and gills of the fish 

 did not come in contact with the water in the vessel. Fishes 

 thus treated lived five liom-s, and the water in the vessel under- 

 went the changes usually produced by respiration. 



Ermann found that the air, in the swimming bladder of lake 

 fish, is deprived of a considerable portion of its oxygen. Biot, 

 on the contrary, found in the swimming bladder of those marine 

 fishes that inhabit deep waters, more oxygen than nitrogen. 

 Humboldt and Provengal observed that after the removal of 

 the swimming bladder fishes continued to absord oxygen, but 

 that they did not form any carbonic acid; they regard it, how- 

 ever, as doubtful whether this phenomenon is due to the pa- 

 thological condition of the animal, or to the absence of the 

 swimming-bladder. 



Insects can live for a long time under the receiver of the 

 air-pump, in a very rarified atmosphere; if, however, their stig- 



' Tliiercliemie, p. 140. 



'^ Treviranus estimates the amount at about 505 less than warm-blood animals of 

 equal bulk would consume. His conclusions are based on the experiments referred 

 to in the text. 



