CHAPTER IV 

 THE BLOOD 



Two liquids of similar nature are found in the body, 

 known as the blood and the lymph. These are closely 

 related in function and together they form the nutrient 

 fluid referred to in the preceding chapter. The blood is 

 the more familiar of the two liquids, and the one which 

 can best be considered at this time. 



The Blood : where Found. The blood occupies and 

 moves through a system of closed tubes, known as the 

 blood vessels. By means of these vessels the blood is 

 made to circulate through all parts of the body, but from 

 them it does not escape under normal conditions. Though 

 provisions exist whereby liquid materials may both enter 

 and leave the blood stream, it is only when the blood 

 vessels are cut or broken that the blood, as blood, is able 

 to escape from its inclosures. 



Physical Properties of the Blood. Experiments such as 

 those described at the close of this chapter reveal the 

 more important physical properties of the blood. It may 

 be shown to be heavier and denser than water ; to have 

 a faint odor and a slightly salty taste ; to have a bright 

 red color when it contains oxygen and a dark red color 

 when oxygen is absent; and to undergo, when exposed 

 to certain conditions, a change called coagulation. These 

 properties are all accounted for through the different 

 materials that enter into the formation of the blood. 



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