RESPIRATION IN FISHES. 275 



For this purpose the water is taken in by the 

 mouth, and forced by the muscles of the throat 

 through the apertures which lead to the branchial 

 cavities: in this action the branchial arches are 

 brought forwards, and separated to a certain dis- 

 tance from each other ; and the rush of water 

 through them unfolds and separates each of the 

 thousand minute filaments of the branchiae, so that 

 they all receive the full action of that fluid as it 

 passes by them. Such appears to be the principal 

 mechanical object of the act of respiration in this 

 class of animals; and it is an object that requires 

 the co-operation of a liquid, such as water, capable 

 of acting by its impulsive momentum in expanding 

 every part of the apparatus on which the blood 

 vessels are distributed. When a fish is taken out 

 of the water, this effect can no longer be produced ; 

 in vain the animal reiterates its utmost efforts 

 to raise the branchiae, and relieve the sense of 

 suffocation it experiences in consequence of the 

 general collapse of the filaments of those organs, 

 which adhere together in a mass, and can no 

 longer receive the vivifying influence of oxygen. 



# 



* It has been generally stated by physiologists, even of the highest 

 authority, such as Cuvier, that the principal reason why fishes 

 cannot maintain life, when surrounded by air instead of water, is 

 that the branchiae become dry, and lose the power of acting when 

 thus deprived of their natural moisture ; for it might otherwise natu- 

 rally be expected that the oxygen of atmospheric air would exert a 

 more powerful action on the blood which circulates in the branchiae, 

 than that of merely aerated water. The rectification of this error is 

 due to Flourens, who pointed out the true cause of suffocation, 

 stated in the text, in a Memoir entitled " Experiences sur le Me- 

 chanisme de la Respiration des Poissons." — Annales des Sciences 

 Naturelles, xx, 5. 



