SMELL. 335 



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 atmospheric air. It is exceedingly ditiicnlt to 

 conceive how matter so extremely rare and subtile 

 as that which composes these odorous effluvia can 

 retain the power of producing any sensible impres- 

 sion on the animal organs ; for its tenuity is so 

 extraordinary as to exceed all human compre- 

 hension. The most copious exhalations from a 

 variety of odoriferous substances, such as musk, 

 valerian, or assafoetida, will be continually ema- 

 nating 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 the 

 nicest balance will not show the smallest increase 

 of its weight from this impregnation. No facts in 

 natural philosophy at^'oid more striking illustra- 

 tions of the astonishing, and indeed inconceivable 

 divisibility of matter, than those relating to odorous 

 effluvia. 



It would appear that most animal and vegetable 

 bodies are continually emitting these subtle effluvia, 

 of which our own organs are not sufficiently deli- 

 cate to apprize us, unless when they are much 

 concentrated, but which are readily perceived and 

 distinguished by the lower animals; as may be in- 

 ferred from their actions. A dog is known to follow 



