248 OUR BODIES AND HOW WE LIVE 



All parts of the body have not this sense of touch in an 

 equal degree. The sense of touch -is most delicate in the 

 tip of the tongue, the tips of the fingers, and the edges of 

 the lips, and least delicate in the middle of the back. 1 



341. Sensations of Heat and Cold. The skin also judges 

 to a certain extent of heat and cold. These sensations can 

 be felt only by the skin and the lining membrane at the 

 entrance to various passages. 



The sensitiveness of the skin to heat and cold varies in 

 different parts of the body. The palms of the hands and 

 the bends of the joints are sensitive parts. A woman holds 

 her iron near her cheek to tell whether or not it is hot. 

 Nurses test the heat of the baby's bath by plunging the 

 elbow into the water. 



Experiment 68. To illustrate the muscular sense. Take two 

 equal iron or lead weights ; heat one and leave the other cold. The 

 cold weight will feel the heavier. 



Experiment 69. To test the sense of locality. Ask a person to 

 shut his eyes ; touch some part of his body lightly with the point of 

 a pin, then remove it, and ask him to indicate the spot touched. 



Experiment 70. Our sensations of heat and cold depend on the 

 temperature of the skin. Place one hand in cold and the other in hot 

 water, then plunge both in lukewarm water. To the cold hand the luke- 

 warm water will appear hot, while to the warm hand it will seem cold. 



1 The sense of touch may be said to belong to every animated being, 

 and is one great characteristic of animal life. In many animals the tongue 

 is an instrument of touch as well as of taste. Certain animals, in addition 

 to the tongue, have special organs of touch, such as the whiskers of the cat 

 and the rabbit. These are really parts of the skin. 



There is no other sense so capable of improvement as that of touch. 

 The blind learn to read with ease by passing their fingers over raised letters. 

 A famous botanist was blind, but was able to distinguish rare plants by the 

 fingers and by the tip of the tongue. The silk weavers of Bengal are said 

 to be able to distinguish, by the touch alone, twenty different degrees of 

 fineness in the unwound cocoons. 



