TOUCH. 197 



touch, by its not requiring, like the latter, any muscu- 

 lar effort for its exercise *. That there are peculiar 

 nerves, in various parts of the skin, appropriated to 

 the perception of heat, Dr. Darwin thinks is proved 

 by the heat of a furnace giving no pain to the nerve 

 of the eye, while it scorches and pains the parts ad- 

 jacent. Warm water, again, or warm oil, when 

 poured into the ear, gives no pain to the nerves of 

 hearing, and its warmth is not even perceived by them, 

 though it may be hot enough to scald the external 

 orifice. He evidently does not, in this, make any 

 account of these nerves being deep-seated. Whether 

 these facts and others of a similar kind are sufficient 

 to authorize us to consider the sense of heat distinct 

 from that of touch, we shall not here stop to determine, 

 but content ourselves with mentioning a few circum- 

 stances illustrative of the subject, in addition to those 

 we have mentioned elsewhere f. 



Amongst birds, fewer instances perhaps are com* 

 monly observed of the peculiar influence of cold and 

 heat than in other animals, in consequence, no doubt, 

 of their warm covering of feathers. We have re- 

 marked also, that the non-conducting power of the 

 feathers is peculiarly increased in some of the smaller 

 species during the night by changing the position. 

 We have at present, for example, an ox-eye (Parus 

 major, RAY), which, when going to sleep, rolls itself 

 into a round ball, erecting every feather so far as not 

 to separate its point from the adjoining ones. The 

 quantity of the non-conducting surface is by this 

 means increased to the depth of nearly half an inch 

 more than it is when the feathers are laid flat and 

 smooth, while the bird is skipping about the cage in 

 the day time ; and as the feathers of the belly are at 



* Philosophy of Zoology, i. 171. 



f Insect Miscel, p. 16, &c, j and Habits of Birds, chap, iii, 



U 



