OF THE SENSE OF SMELL. 105 



sitive skin beneath. It deadens more or less all impressions, 

 and hence its thickness on the heel and sole of the foot 

 generally : it thickens whenever it is exposed to friction. 

 Finally, in some animals it becomes encrusted with calcareous 

 matters, becoming then altogether inflexible, and rendering 

 the surface of the body insensible. 



209. The sensibility of the skin resides in the dermis, 

 and depends on the nerves of touch distributed to the 

 papillae. 



210. Special Organs of Touch. Tactile sensibility is 

 spread over the whole body, but it is in the extremity of the 

 fingers alone that the true power of touch resides. The hand, 

 of course, is especially made for the exercise of this faculty. 

 The delicacy of the integuments, the length of the fingers, 

 and the opposing thumb, all contribute to this effect. 



In most animals these organs are not so favourably 

 arranged : nevertheless, the proboscis of the elephant is a 

 wonderfully tactile instrument. There are animals which em- 

 ploy the tongue for this purpose, and others are provided with 

 palpi, tentacula, &c. (Figs. 7, 8), 



211. By touch we appreciate most of the physical pro- 

 perties of bodies, such as their dimensions, form, temperature, 

 consistence, polish or the opposite, weight, movements, &c. 

 Some philosophers have adopted exaggerated ideas of the 

 importance of this sense to human intelligence, for which 

 there is not the slightest occasion. 



OF THE SENSE OF TASTE. 



212. By this sense we discover the savours of bodies. 



213. Certain bodies are extremely sapid, others but 

 little, and some not at all. The cause of these differences is 

 quite unknown ; but,, generally speaking, insoluble bodies are 

 not sapid, and when the tongue is dry and parched the taste 

 is not perceived. 



214. By taste most animals distinguish their food ; and 

 hence, no doubt, the reason why the instrument is placed at 

 the entrance of the digestive tube. The tongue is the prin- 

 cipal seat of taste ; but other parts of the mouth possess the 

 power of perceiving certain savours. The mucous membrane 

 which covers the tongue of man is sufficientl}" well supplied 

 with bloodvessels and nerves supplying papillae of various 



