THE SKIN 



325 



The pigments are the secretory products of certain cells of the connec- 

 tive-tissue class, but differentiated further for this special purpose. In 

 some of the "lower" animals these cells have distinct ameboid retraction - 

 and-expansion movements described somewhat in the chapter on Proto- 

 plasm. A tendency to this perhaps is seen in the going and coming of 

 freckles and tan and especially in the quick blanching of the hair of 



FIG. 180 



Hair-follicle showing its unstriated muscles and the sebaceous gland: 1, the hair-root; 2, its 

 bulb embracing the papilla of the hair-follicle; 3, internal sheath of the root, and 4, external 

 sheath; 5, tunic of transverse fibers of the follicle; 6, tunic of longitudinal fibers; 7, unstriated 

 muscles inserted in the latter layer; 8, their free ends, losing themselves in the superficial 

 strata of the skin; 9, multilobular sebaceous gland; 10, excretory duct of same; 11, simple 

 sebaceous gland; 12, mouth of the hair-follicle. (Sappey.) 



the head (e. g., Henry M. Stanley in the African forest of the Pigmies) 

 under the emotion of terror or from the more chronic emotional condition 

 of worry and trouble. 



At least two biological functions are served by surface-pigmentation 

 in man, namely, to make the body more beautiful and to protect its 

 protoplasm from excessive sun-light. 



Biologically the former function, that of ornamenting the body, is a 



