BLOOD 217 



BLOOD 



The blood is contained in the bloodvessels, which 

 are practically a closed arrangement of tubes the 

 arteries, veins, and their connecting capillaries. 



Function. The function of the blood is to transmit 

 the various nutritive elements, absorbed from the 

 organs of digestion to the tissues of the body, to carry 

 to the tissues oxygen absorbed from the air in the 

 lungs; to remove from the tissues the various waste 

 products, such as urea, uric acid, water through the 

 kidneys and skin, carbon dioxide (CO 2 ) the latter 

 being carried to the lungs by the red cells which give 

 it off with the expired air; to maintain the temperature 

 of the body in warm-blooded animals. 



. Physical Characteristics. Blood is alkaline in reac- 

 tion, opaque in color, and appears as a homogeneous 

 mass. Two kinds of blood are contained in the vascular 

 system in the arteries it is bright red in color, while 

 in the veins it is dark bluish in color. The color of 

 the blood is due to the coloring matter hemoglobin 

 contained in the red cells. The bright red color of 

 normal blood is due to the hemoglobin in combination 

 with the oxygen, which it absorbs on coming in contact 

 with the air in the lungs. The bluish color of venous 

 blood is due to the hemoglobin absorbing the carbon 

 dioxide from the tissues a waste compound which is 

 being carried to the lungs to be given off in the expired 

 air. 



Constituents of Blood. It consists of a liquid por- 

 tion called the liquor sanguinis or plasma, red cells 

 or erythrocytes, white cells or leukocytes, and blood 

 plaques. (Of course the latter can only be seen with 

 the microscope.) 



The Plasma. This is a clear, slightly yellowish, 

 transparent fluid, consisting mostly of the nutritive 

 elements of the foods proteins, carbohydrates, fats, 

 inorganic salts which have been rendered possible 



