GLANDS AND THE WORK OF EXCRETION 2O7 



entire surface of the body. A typical sweat gland consists 

 of a tube which, starting at the surface of the cuticle, 

 penetrates to the under portion of the true skin and there 

 forms a ball-shaped coil. The coiled 

 extremity, which forms the secreting 

 portion, is lined with secreting cells 

 and surrounded by a network of capil- 

 laries. The portion of the tube pass- 

 ing from the coil to the surface serves 

 as a duct (Figs. 91 and 121). 



The sweat glands secrete a thin, 

 colorless fluid, called perspiration, or 

 sweat. This consists chiefly of water, 

 but contains a small per cent of salts 

 and of urea. The excretory work of 

 these glands seems not to be so great 

 as was formerly supposed, but they 

 supplement in a practical way the 

 work of the kidneys and, during 

 diseases of these organs, show an in- 

 crease in excretory function to a 

 marked degree. The 



b \ 



FIG. 91. Diagram 

 of section through a 

 a. Outer 



forming the coiled portion 

 of the gland. c. Duct 



perspiration sweat 2 land - 



also aids in the regulation of the 'ayer of skin or cuticle. 

 b. Dermis or true skin. 



temperature of the body (Chapter dj , sections of the tube 

 XVI). 



Excretory Work of the Lungs. 



IT 71 -i ,i -i , i ij passing to the surface. 



While the lungs cannot be regarded -T 



The other structures of 



as glands, they do a work in the re- t he skin not shown. 

 moval of waste from the body which 

 must be considered in the general process of excretion. 

 They are especially adapted to the removal of gaseous 

 substances from the blood, and it is through them that 

 most of the carbon dioxide leaves the body. The lungs 



