BOOK IX 



THE FUNCTIONS OF THE SKIN AND BODY 

 TEMPERATURE 



CHAPTER LVII 

 THE FUNCTIONS OF THE SKIN 



ONE function of the skin is to confine and support the soft parts 

 with a strong, pliable, elastic cover, and protect them from harm. 

 Its structure is adapted to these functions. The skin, by virtue of 

 its blood -supply and sweat glands, also plays a great part in regu- 

 lating the temperature of the organism, and by virtue of special 

 nervous structures affords information of the nature of the surround- 

 ings in which the organism finds itself. 



The skin, in addition, acts as an organ of excretion, and to a 

 certain extent as an organ of absorption. In some animals, the skin 

 serves a respiratory function. 



The skin consists of two parts the epidermis, or outer skin, and 

 the cutis vera (true skin), or corium. The epidermis consists of 

 stratified squamous epithelium, and has no bloodvessels. The most 

 external layer is known as the stratum corneum, or " horny layer." 

 Its cells are largely composed of keratin, and are of a scaly nature. 

 This layer is particularly thick in the palms of the hand and soles, 

 of the feet. The next layer inwards is known as the stratum lucidum. 

 Its cells appear clear and free from granules. Within this layer is 

 another, known as the stratum granulosum. Its cells are charac- 

 terized by the presence of granules of eleidin, a substance which 

 stains deeply with hsematoxylin. Beneath this comes the deepest 

 layer of the epidermis the rete mucosum. or stratum Malpighii (the 

 Malpighian layer), the cells of which are not horny, but protoplasmic 

 in nature. It is in this layer that there is deposited the pigment 

 melanin, which gives a characteristic black colour to the skin of the 

 dark races. The cells are in more than one layer, those in the 

 deepest are columnar, those above polyhedral in shape. They multiply 

 in the deepest layer, and are gradually pushed out, and undergo the 

 change into horny matter as the older layers are worn off. Tissue 

 lymph soaks between the cells, and keeps up the transpiration of 



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