10 THE ANGLER-NATURALIST. 



are allowed to do so. The great majority of fishes, how- 

 ever, cannot continue to breathe in atmospheric air alone 

 beyond a very limited period, as, without the aid of fluid, 

 the gill-filaments shortly become stuck together, when of 

 course the air cannot pass between them, and they lose 

 the power of imbibing oxygen. Hence the gasping of 

 fishes out of water, which is the effort of Nature to sepa- 

 rate the gill-filaments. 



Temperature of Blood. 



The consumption of oxygen in all fishes is comparatively 

 small, which may be the cause of the cold nature of their 

 blood; and the temperature of the bodies of fish that swim 

 near the bottom is seldom more than two or three degrees 

 higher than that of the water at its surface*. In surface- 

 swimmers a temperature of 10 Fahr. above that of the 

 water has been occasionally found ; and it may be received 

 as a general law, that those fish which swim near the surface 

 have a high standard of respiration (and therefore of tem- 

 perature), die rapidly on being taken out of water, and 

 have flesh prone to quick decomposition, and vice versa. 



* A very ingenious application of this principle lias lately been 

 made, by the invention of a machine for re-oxygenating the water in 

 bait-kettles, vivaria, &c. The apparatus is composed of a tube formed 

 in the shape of the letter T, to the perpendicular of which an india- 

 rubber air-ball, or a pair of bellows, is attached. The transverse portion 

 of the tube is pierced full of minute holes, which, being placed in the 

 kettle, the air, upon pressure of the ball, is forced out into the water, 

 which is thus made fit for respiration. 



