THE SKIN 



various chemical substances in the blood, so that one gland 

 secretes oil, another perspiration, another saliva, etc. The 

 kidneys are important glands which resemble some of the 

 glands of the skin in that they secrete injurious substances 

 that must be removed from the system. Secretion is the 

 name given the various fluids formed by glands. Excre- 



FIG. 15. 



A divided saccular gland with duct, d. 



FIG. 16. 



A similar gland more divided. 



FIG. 17. 



A racemose or branching gland, part only 

 being shown. 



More Diagrams to illustrate the Structure of Glands. 



tion is a secretion of harmful substances to be removed 

 from the body. 



17. Secretion is not simply a process of soaking or sift- 

 ing through. The walls of the glands are made of cells. 

 The cells, those wonderful little bodies which we shall study 

 more carefully in another chapter, obtain from the blood 

 the materials which they secrete. More than this, by the 

 aid of the nerves, they can regulate the amount of secretion 



