170 



SMELLING, 



Emily. But, Dr. B., do fishes possess the organ of 



hearing ? 



Dr. B. Fishes probably surpass all other animals 

 in acuteness of hearing ; owing in some measure per- 

 haps, to the nature of the medium through which the 

 vibrations are conveyed. Water, you know, must be a 

 much better medium for conveying sounds, than air. 

 Some few fishes, in fact, possess the rudiments of an 

 external ear. 



Emily. Some of the inferior animals have one ad- 

 vantage over us, in the structure of their hearing organs. 

 They can change the position of their external ear, so 

 as to correspond to the direction whence the sound pro- 

 ceeds. This is particularly manifest in the horse, rab- 

 bit, &c., and these animals, if 1 mistake not, have the 

 sense of hearing extremely acute. 



Dr. B. Of the remaining senses, we have but little 

 to say, as the organs are extremely simple, and their 

 functions can be observed by all. Smelling is the sen e 

 which makes us acquainted with the presence of certain 

 particles given off and diffused to various distances, from 

 odorous bodies. " The smelling apparatus may be com- 

 pared to a sieve placed in a spot, over which the current 

 of air that is introduced into the chest in respiration, 

 passes, and which is destined to detain all the foreign 

 bodies which may happen to be mixed with the air, par- 

 ticularly odours. This apparatus, in the first place con- 

 sists of the pituitary membrane, which lines the back 

 part of the nostrils and other cavities which communicate 

 with them." On this membrane, are distributed the mi- 

 nute and numberless ramifications of the olfactory nerve, 

 or the nerve of smell. By this, the impressions made 

 on the membrane, are communicated to the brain. In 

 order to protect this delicate expansion of nerves thus 

 freely exposed to the air and to the painful stimulus of 

 acrid and pungent odours, the membrane is kept con- 

 stantly moist by a secretion of mucous ftuid from the 

 glands, with which it is provided. The sense of smell 



