INTRODUCTION. 



air through the medium of water. Air is the 

 pabulum vita equally of the fish and the 

 fisher, but with a difference which at first 

 sight fills our minds with astonishment ; for 

 reverse their several positions, and death is 

 the inevitable consequence. When we say 

 fish breathe through the medium of water, we 

 assert what is readily demonstrable : for im- 

 merse a fish into distilled water, which is only 

 water deprived of its air, and such fish dies 

 as quickly as a man submerged. Water, in 

 its natural state, restores to the blood of fishes 

 its vital and arterial qualities, by means of 

 the oxygen contained in the air, which the 

 water holds in suspension ; the machinery for 

 this purpose, in fishes, being within the gills, 

 as in ourselves it is within the lungs. Their 

 organisation, like that of quadrupeds, is sup- 

 ported by means of a skeleton, either bony 

 or cartilaginous ; and their motions are effected 

 by muscular masses, nourished by red, but 

 cold blood ; such muscular masses being, as 

 in ourselves, excited into action by nervous 

 influence derived from a brain, and distributed 

 by means of a spinal rope of medullary matter. 

 The extremities of quadrupeds are represented 

 in fishes by fins, which perform their mo- 

 tions with surprising strength and celerity. 



