Touch. 423 



in addition arc also white under their tails. The bleaching of tho skin 

 of northern races of men may be due in some degree to their wearing 

 clothes. This conjecture is confirmed by the fact that the protean sala- 

 manders found in the underground lakes of Carniola, besides being des- 

 titute of eyes, are nearly white. If exposed to light they seem to suffer, 

 and their skin seems to become colored. They are undoubtedly from a 

 colored ancestry and have been bleached by seclusion. 



CHAPTER XLV. 



TOUCH. 



The earliest, most common, indeed the universal sense is the sense of 

 touch, including under this head the various subdivisions of the sense 

 that depend on the stimulation of the skin. Every animal in existence, 

 and some plants, possess this sense, which cannot be said of any other 

 sense ; and from it every other sense has been differentiated. It is no 

 more inevitable that an animal should possess an outside, than that the 

 outside should constantly come into contact with and be stimulated by 

 objects external to itself, that is, its environment. It is the essential 

 characteristic of protoplasm, as well as its products, to become more 

 yielding and pliant to a stimulus that is able to move it without 

 violence, the of tener and more habitually the stimulus acts ; while, if the 

 stimulus is violent without being destructive, excessive tissue is depos- 

 ited at the stimulated point, the part hardens and its sensitiveness is 

 lessened. The whole external part of the animal body is constantly in 

 contact with some object the ground, the air or the water. And in the 

 course of its locomotion it may meet with and be arrested by many ob- 

 stacles. The stimulus of gentle contact begets sensitiveness in the parts 

 stimulated. This is first alike over the whole body in the case of simple 

 aquatic animals. Later it becomes specialized in the projecting parts of 

 of the body limbs, tail and head. Later the limbs or their ends may 

 through excessive stimulation become calloused and finally armed with 

 nails or hoofs, &c. , while the head with its appendages of snout, tongue 

 or tentacles, &c. , becomes more sensitive from the habit of more fre- 

 quent stimulus of the proper degree of activity and force. Probably 

 the general skin does not in any animal lose the whole of its sensitive- 

 ness, but it becomes relatively less in the skin in the ratio in which it is 

 increased in special organs. 



The skin consists of two principal layers. ( 1.) The epidermis, cuti- 

 cle, or horn-plate, and ( 2 ) the dermis, corium, or true skin. This second 

 bottom layer rests upon the cellular connective tissue which often con- 



