Blood and its Ftinctions 143 



amined with a microscope, it is seen to be a compar- 

 atively clear liquid in which float numerous reddish, 

 disk - like bodies. These bodies, which are known 

 as corpuscles, give to the blood its bright red color. 

 The liquid in which they are suspended is called the 

 plasma. 



The corpuscles are not mere masses of unformed 

 matter, but they are minute bodies having a definite 

 form and structure. They make up from 35 to 40 per 

 cent of the blood, and contain over 30 per cent of dry 

 matter. This dry matter consists mostly of haemo- 

 globin, a compound that is peculiar to the blood and 

 equips it for one of its most important offices. Haemo- 

 globin, as before stated, is made up of a proteid (globin) 

 and a coloring matter (hfematin), in the latter of which 

 is combined a definite proportion of iron. The peculiar 

 property of this compound, which renders it so useful 

 a constituent of the blood, is its power of taking up 

 oxygen and holding it in a loose combination until it 

 is needed for use. When thus charged, it is known 

 as oxyhaemoglobin. Because of this function of their 

 most prominent constituent, blood corpuscles become 

 the carriers of oxygen to all parts of the body. There 

 are reasons for believing that they are also chiefly con- 

 cerned in gathering up one of the waste products of 

 the nutritive changes, viz., carbon dioxid, and convey- 

 ing it to the points where it may be thrown off from 

 the body. 



The plasma is about nine-tenths water, so that it 

 easily holds in solution whatever soluble nutrients are 

 discharged into it from the alimentary canal. Among 



