NUTRITION. 109 



material be replaced by new. Not merely must matter for 

 assimilation be provided, but the various waste products 

 must be removed. Here again the blood-vessels and ab- 

 sorbents come into play. Absorbents are found not only 

 in the walls of the alimentary canal, but all over the body. 

 The wastes of each working tissue are passed out into 

 them, and by them carried into the blood-vessels; these 

 in turn carry the wastes to the lungs, kidneys, and skin, 

 which get rid of them. The blood is thus as important 

 in relation to removing the waste matters of an organ as 

 in regard to supplying it with food and oxygen. 



Nutrition. From what has been said above it is clear 

 that the nourishment of the body is a very complicated 

 process. It implies (1) the. reception, of food from out- 

 side ; (2) the digestion of food ; (3) the absorption of 

 digested food ; (4) .the conveyance of absorbed food to all 

 parts by the blood; (5) the_ taking up of wastes from the 

 different organs ; (6) the conveyance of these wastes by the 

 blood to excretory organs which pass them out of the body ; 

 (7) the absorption of oxygen in the lungs, and its con- 

 veyance by the blood to every organ ; (8) assimilation or 

 the building up of new tissue from materials brought by 

 the blood ; and (9) disassimilation, or the breaking down 

 of working tissues by combination with oxygen. 



In subsequent chapters we shall have to consider in 

 more detail, Digestion, Circulation, Absorption, Respira- 

 tion, and Excretion. The sum total of 4he actions of all 

 the organs concerned in the nourishment of the body is 

 known as the function of nutrition. 



Where do we find absorbents in addition to those of the alimen- 

 tary canal? What is their function? What part does the blood 

 play in the removal of wastes? 



Enumerate the processes concerned in the nourishing of the body 



What is meant by the function of nutrition? 



