HOW TIIK ANIMAL I.IVP'.S 'J 1 1 



♦bo blood the socrotion ^vhic'h that ;^hiii(i is uj»- 

 pomted to furnish, and pour it out through tho 

 gland ducts. Tho secretion from one j^hin<l is 

 nutritious, as in the c'as«» of milk ; that from 

 another is digestive, as in the s«M*n'tion of th«» 

 stomach; and from a tliinl it is wasto matter, like 

 sweat. The selection from th«> nutritive liquid of 

 the l)lood is the work of the individual rdls, an<l 

 is always the same for each kind of gland. 



364. The cells of some glands construct a n»'w 

 substant'c, which is not secreted hut jiouhmI hack 

 into the blood. Thus the liver makes glycogen, 

 which passes into grape sugar, and serves for 

 the production of heat, nniscular work and nu- 

 trition. 



3(3.j. Some cells on the walls of the intestines 

 absorb nutritive and other matters from the 

 liquid contents of the bowels and pass them on 

 into tho circulating (blood and lymph) vessels. 



300. Besides these cells which become im- 

 prisoned in their particulai' tissues, and the work 

 of which is restricted to tho conducting of the 

 growth or other functions of such tissues, there 

 is a large class which floats free in the liquids 

 of the body. The rod ami white IjIimkI glo)»- 

 ules and lymph cells are examples. These 

 globules or corpuscles circulate in all parts of 

 the body, thus suggesting the freedom of the 

 one -celled animal. Hut limitations have l^^en 



