NUTRITION 



215 



while excretion, of necessity, removes the dead waste from these, lest it 

 poison them. Nutrition then is more than metabolism, and constitutes 

 a definite subject of great importance because at the basis of every 

 vital process. Our discussions of protoplasm and of food are intro- 

 ductory to the descriptions of this chapter, yet do not infringe on its 



Fio. 112 



Absorption 



carbon, 

 dioxide 



water. 



miter, 

 detnius. 



External nutrition. The upper picture suggests the places of absorption of the various proxi- 

 mate principles into the villus. The lower part of the figure indicates diagrammatically the 

 various excretory organs and what chiefly passes out through each. 



province of trying to explain how the food renews the ever-wasting 

 body and supplies it with energy. 



Nutrition, like respiration, is, for descriptive purposes, of two sorts, 

 external and internal. External nutrition is that part of the total process 

 by which, on the one hand, the blood receives its nutritious elements, and 

 loses its excrementitious portions, on the other. The former enter it from 

 the gut, while the latter leave it by way of the various excretory organs. 



