314 THE BLOOD AND ITS CIRCULATION 



of the body is also due to the blood, which brings to the surface of 

 the body much of the heat given off by oxidation of food in the 



muscles and other tissues. When 

 the blood returns from the tissues 

 where the food is oxidized, the 

 plasma brings back with it to the 

 lungs part of the carbon dioxide 

 liberated where oxidation has taken 

 place. Some waste products, to be 

 spoken of later, are also found in 



Human blood as seen under the t/ ^ ie Pl asma - 

 high power of the compound The Red Blood Corpuscle ; its 



Structure and Functions. - The 

 red corpuscle in the blood of the 

 frog is a true cell of disklike form, containing a nucleus. The red 

 corpuscle of mail is made in the red marrow of bones and in 

 its young stages has a nucleus. In its adult form, however, 

 it lacks a nucleus. Its form is that of a biconcave disk. So 

 small and so numerous are these corpuscles .that about five 

 million are found in a cubic millimeter of normal blood. They 

 make up almost one half the total volume of the blood. The 

 color, which is found to be a dirty yellow when separate cor- 

 puscles are viewed under the microscope, is due to a protein 

 material called haemoglobin. Haemoglobin contains a large amount 

 of iron. It has the power of uniting very readily with oxygen 

 whenever that gas is abundant, and, after having absorbed it, 

 of giving it up to the surrounding media, when oxygen is there 

 present in smaller amounts than in the corpuscle. This function 

 of carrying oxygen is the most important function of the red 

 corpuscle, although the red corpuscle also removes part of the 

 carbon dioxide from the tissues on their return to the lungs. The 

 taking up of oxygen is accompanied by a change in color of the 

 mass of corpuscles from a dull red to a bright scarlet. 



Clotting of Blood. If fresh beef blood is allowed to stand overnight, 

 it will be found to have separated into two parts, a dark red, almost solid 

 clot and a thin, straw-colored liquid called serum. Serum is found to 

 be made up of about 90 per cent water, 8 per cent protein, 1 per cent 



