INSTINCT OF FISH. 147 



health, they must be exquisitely sensible to 

 changes in water, and must have similar 

 relations to it, that an animal with the most 

 delicate nasal organs has to air. A vulture 

 or a dog scents not only particular food and 

 particular game at great distances, but even 

 makes of the smell a kind of language ; and 

 I doubt not that when dogs that have been 

 blindfolded and carried away from their 

 home, return to it, it is by the sense of 

 smell: to them each town, lane, or field, 

 must have a particular smell. And I have 

 seen even a blind horse, an animal in which 

 the sense of smell is less acute, evidently 

 find his way by his sense of smell, to his 

 master's house and stable, which was, in- 

 deed, near a tan-yard. The state of parts 

 of water in the sea or great lakes produced 

 by the impregnations carried down by par- 

 ticular streams, is much more permanent 

 than a like state in air: so that though the 

 knowledge given by the nasal organs may 

 be more easily communicated at a distance 

 by winds, yet that produced by streams on 

 the bronchia? of fishes is more invariable, 



l 2 



