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CHAPTER IV. 



SMELL. 



ANIMAL life being equally dependent upon the salubrious 

 qualities of the air respired, as of the food received, a sense 

 has been provided for discriminating the nature of the for- 

 mer, as well as of the latter. As the organs of taste are 

 placed at the entrance of the alimentary canal, so those of 

 smell usually occupy the beginning of the passages for res- 

 piration, where a distinct nerve, named the olfactory ', ap- 

 propriated to this office, is distributed. 



The sense of smell is generally of greater importance to 

 the lower animals than that of taste; and the sphere of its 

 perceptions is in them vastly more extended than in man. 

 The agents, which give rise to the sensations of smell, are 

 certain effluvia, or particles of extreme tenuity, which are 

 disseminated very quickly through a great extent of atmo- 

 spheric air. It is exceedingly difficult to conceive how mat- 

 ter so extremely rare and subtle as that which composes 

 these odorous effluvia can retain the power of producing any 

 sensible impression on the animal organs: for its tenuity is 

 so extraordinary as to exceed all human comprehension. 

 The most copious exhalations from a variety of odoriferous 

 substances, such as musk, valerian, or asafoetida, will be 

 continually emanating for years, without any perceptible 

 loss of weight in the body which supplies them. It is well 

 known that if a small quantity of musk be enclosed for a 

 few hours in a gold box, and then taken out, and the box 

 cleaned as carefully as possible with soap and water, that 

 box will retain the odour of musk for many years; and yet 



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