SMELL IN INSECTS. 59 



singular boy, Mitchel, born deaf and blind, had the 

 same faculty of distiguishing persons by smell *. 



The most close analogy, however, to the smell of 

 ants, is furnished by various hounds, which can track 

 unerringly, by the odour left on the grass, the path of 

 hares, foxes, and other animals, and by that means 

 discover their lurking-place. An instance of the 

 almost miraculous acuteness of smell in the blood- 

 hound is related by Boyle. " A person of quality," 

 he says, " to make trial whether a young blood- 

 hound was well instructed, caused one of his ser- 

 vants to walk to a town four miles off, and then 

 to a market-town three miles farther. The dog, with- 

 out having seen the man he was to pursue, followed 

 him by the scent to the above-mentioned places, not- 

 withstanding the multitude of market people that 

 went along the same way, and of travellers that had 

 occasion to cross it ; and when the blood-hound came 

 to the chief market-town, he passed through the 

 streets, without taking notice of any of the people 

 there, and left not fill he had gone to the house 

 where the man he sought rested himself, and found 

 him in an upper room, to the wonder of those that 

 followed him t." The very subtle nature of odours, 

 however, tends to strip these instances of sagacity of 

 their apparent magic ; for a particle of camphor, less 

 than the two-millionth part of a grain, has been 

 found distinctly perceptible to smell J. This has led 

 Von Walther and others into the opinion, that odours 

 are analogous to heat, light, and magnetism; in 

 support of which they urge many very curious and 

 plausible arguments. The French chemists, on the 

 other hand, consider aroma as a distinct element $. 



* See Wardrop's Account, 

 t Boyle on the Nature of Effluvia, chap. iv. 

 I Haller, Elementa Physiol., vol. v. p. 58, 4to. 

 Rennie's Supp, to the Pharraacop, 4rt, droma, 



