134 PHYSIOLOGY. 



through the dermis, is coiled up in a ball in the connective 

 tissue lying just underneath the inner skin. The cells 

 forming the walls of the coiled part differ from those of 

 the duct, or straighter part of the tube. As the blood 

 flows around the coil it gives off lymph, and from the 

 lymph the cells of the gland take certain waste matters, 

 which are passed out to the surface of the skin. There is 

 also some muscular tissue around the walls of the gland. 



Model of a Sweat Gland. Take a small rubber tube a foot long ; 

 close one end ; tie the half with the closed end into a globular knot ; 

 around and between the coils place a network of red cord to represent 

 the blood capillaries, as there is a rich supply of these blood tubes 

 around the coil. 



The Essential Features of a Gland. i. Cells lining 

 a cavity, the cells having the power of taking something 

 from the blood (or lymph). 



2. Blood supply or lymph supply. 



3. A duct or tube to pour out on some surface the 

 liquid taken from the lymph. 



4. Nerves to the cells by which their action is controlled. 



5. (Probably) Special nerve centers controlling the 

 various glands. The cells of the glands in many cases 

 so alter the substances taken from the blood that what is 

 produced by the gland differs from anything found in the 

 blood. The gland may be said to manufacture the liquid. 



The Relation between Glands and the Blood 

 Supply. The sweat glands, like all glands, are largely 

 dependent on the amount of blood supply. In exercising, 

 the skin is usually redder from the greater blood supply, 

 and at the same time the glands are more active ; for, 

 during exercise, and immediately after it, there is more 

 waste matter to be thrown out. But the activity of the 

 gland is not a mere filtering process, due to the greater 



