CHAPTEE IX 



THE SKIN AND CUTANEOUS GLANDS 



CONTENTS. 1. Structure of the skin and continuous desquamation of the 

 stratum corneum. 2. Coiled sweat glands and sensible and insensible cutaneous 

 secretion. 3. Chemical substances excreted in perspiration. 4. Innervation of sweat 

 glands. 5. Sebaceous glands and specific formation of sebum. 6. Mammary 

 glands. 7. Chemical composition of milk. 8. Influence of diet on the secretion 

 of milk. Origin of secretory products. 9. Histological and chemical processes of 

 milk formation. 10. Influence of nervous system on the milk secretion. 11. 

 Absorption by the skin. Bibliography. 



THE body suffers considerable loss of material by the skin, as well 

 as from the lungs, intestine, and kidneys. But this loss consists 

 only to a minimal extent in katabolic products. As an excretory 

 organ and blood purifier, the skin (by the glandular secretions 

 which it pours out) is therefore of secondary importance. Its 

 functions as a protective organ are far more significant. It not 

 only regulates the internal heat and adapts it to the external 

 environment, lubricates the stratum corneum of the epidermis and 

 the hair, and renders them elastic, but it further provides the 

 fittest nutriment for the new-born animal, which is the most 

 fundamental form of protection of the species. 



In this chapter we shall deal with the skin, not as the seat of 

 the sense-organs (which will be fully discussed in Vol. IV.), but only 

 as an external integument, provided with innumerable glands by 

 which the body suffers loss, either in the form of gas and vapour 

 (perspiration), of water (sweat), of adipose and horny substances 

 (sebaceous and ceruminous secretions, epidermoid desquamation), 

 or of an alimentary fluid (milk secretion). Each of these products 

 has a distinct physiological significance and special character 

 which it must be our task to determine. Lastly, we shall discuss 

 the question whether, and how far, the skin may be regarded as 

 an absorbing surface. 



I. Without entering into details of the minute structure 

 of the skin, the interest of which is mainly morphological, we 

 shall confine ourselves to stating that two principal layers can be 

 distinguished, the epidermis (or cuticle), and the derma (cutis 



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