ABSORPTION OF NUTRIENTS 31 



Circulation of the Blood. The blood is kept in 

 circulation by the continuous pumping of the heart. 

 In this way the blood is forced along the arteries on its 

 outward journey, and after the blood has passed through 

 the various organs of the body, it returns to the heart 

 along the veins. Whenever the blood passes through 

 an organ in the body, e.g., liver, kidneys, etc., the 

 blood-vessel divides up into a large number of very fine 

 blood-vessels (capillaries), which gradually come together 

 into one large vessel as the blood leaves that organ. 



The object of this subdivision of the blood-vessel 

 into very small vessels as it passes through an organ is, 

 first of all, to get the walls of the blood-vessels so small 

 in the organ that nutrient liquids may pass into the 

 blood (small intestines, and to some extent, stomach), 

 or that impurities may be taken out (lungs, kidneys, 

 etc.). Further, the blood may be utilised for the 

 manufacture of digestive juices (liver, pancreas, etc.) ; 

 or, in fact, some of the nutrients in it may be stored up 

 temporarily, as in the case of glycogen in the liver. 



We can now explain the functions of the various 

 nutrients in the animal body. 



X. FUNCTIONS OP POOD NUTRIENTS IN 

 ANIMAL BODY. 



It is usual to regard the protein (crude 

 albuminoids), fats, and carbohydrates as the chief 

 nutrients in foods, but it will be necessary to refer 

 to the fibre and mineral matter in addition, as they 

 play a not unimportant part in animal nutrition. 

 Further, the part played by water in dissolving the 

 nutrient material, thus enabling it to be absorbed into 



