THE KIDNEYS AND THE URINE. 73 



face with the exception of the palms and soles, and most abun- 

 dantly in the hairy parts. They are intimately connected with 

 the hair-follicles, and their ducts, as a rule, open into the folli- 

 cles, though sometimes they discharge separately. The glands are 

 aggregate glands ; that is, are formed by the subdivision of the duct 

 to make up the lobules of the gland. There is a delicate plexus 

 of capillary vessels about the sacculi. 



What do they secrete? 



The secretion of the sebaceous glands is a soft, oily, white mate- 

 rial, and has, besides other fats, stearin for basis. Its use seems to 

 be to lubricate the skin, keeping it soft and flexible, and at the same 

 time, by its oily nature, to prevent maceration of the skin by con- 

 tinued 'exposure to moisture, and to check the undue absorption 

 from the surface. Sebaceous matter is not excrementitious, but 

 is a secretion. 



Has the skin power to absorb ? 



It has. This function of the skin is utilized in the application 

 of medicines, of food, and of drink in appropriate cases. 



What further function has the skin ? 

 That of regulation of body -temperature. 



THE KIDNEYS AND THE URINE. 

 Describe the gross appearance of the kidneys. 



The kidneys are glandular organs having somewhat the form of 

 a bean. In size they are somewhat more than 4 inches in length, 

 somewhat more than 2 inches wide, and about 1 inch thick. The 

 weight of each organ is about 4 to 6 ounces. A thin but rather 

 tough capsule invests the kidney (Fig. 17). This may be pulled 

 off readily, leaving the surface of the organ smooth and even and 

 of a deep-red color. If a vertical section of the organ be made, 

 the central cavity (sinus) will be noticed, and about it the kidney 

 tissue. Within the sinus are the apices of pyramidal projections, 

 about ten in number, and if the cut surface be examined closely it 

 may be noted that the outer (cortical) portion diifers in appearance 

 from the more central (medullary) portion. The blood-supply is 

 from the renal artery, and the nerve-supply is from the sympathetic 

 system through the solar plexus. 



