6 FOOD OF FISHES. 



with great readiness, not to say greediness ; however, 

 bread should be given sparingly, lest, turning sour, it 

 corrupt the water. They will also feed on the water 

 plant called duck's meat (Lemna), and also on small 

 fry." 



As fishes do not breathe, and are not furnished with 

 lungs, all of them probably derive from the air in 

 water a greater proportion of nutriment than is done 

 by warm-blooded animals, the small red points on the 

 outer edge of the gills having the power to take up 

 oxygen, and probably nitrogen, while they at the same 

 time give off carbonic acid gas *. Be this as it may, 

 the power of very rapid digestion, which has been 

 brought to explain the absence of food in the stomachs 

 of herring and salmon, is certainly an unfounded sup- 

 position, inasmuch as the rapidity of digestion must 

 always depend in a great measure upon a considerable 

 degree of heat, and the natural heat of fishes is always 

 very low. M. Broussonet found, upon several trials, 

 that this heat was from three fourths to one half a 

 degree of Reaumur higher than the water ; and M. 

 Despretz' experiments gave very nearly the same 

 result. 



To me it appears much more probable, that, like 

 reptiles, such as the snake and the frog, fishes have 

 intervals more or less extended of fasting, after which 

 they eat with great voracity, and then rest again for 

 similar intervals without eating. It is almost incredi- 

 ble how long a serpent may be kept alive without food ; 



(1) See " ALPHABET OF SCIENTIFIC CHEMISTRY," p. 105, &c. 



