CHAPTER XII 

 A STUDY OF THE SKIN AND THE KIDNEYS 



Characteristics of the Skin. 1 The whole outer surface of 

 our bodies is encased in a flexible, elastic skin of varying 

 thickness and texture. In regions like the palm of the hand 

 and the sole of the foot, for instance, the skin is thick and 

 tough ; the covering of the lips, on the other hand, is ex- 

 tremely thin. Over the distal bones of the fingers and toes 

 are the nails, and all parts of the body, with the exception 

 of the palms of the hands and the soles of the feet, are 

 covered with hair. Both the hair and the nails are modified 

 parts of the skin. 



Uses of the Skin. The most obvious use of the skin is 

 the protection it affords for the muscles and other organs 

 that lie beneath. In the second place, it has a countless 

 number of sense organs which receive messages from the 

 outside of the body. These are hurried in along nerve fibers 

 to the spinal cord and brain ; and in this way we get impres- 

 sions of temperature, of pressure, and of pain. Again, by 

 means of the perspiratory action of the skin, the body 

 throws off a great deal of water and small quantities of 

 other waste matters. And, finally, as a result of the evapo- 

 ration of this water from its outer surface, the body loses its 

 surplus of heat, and so keeps an even temperature of 981 F. 



As we might infer from all these uses, the skin is a com- 

 plex organ composed of several tissues. We shall now study 

 its structure and see how it is adapted to perform the four 

 functions we have just enumerated. 



1 See " Laboratory Exercises," No. 42. 

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