THE SOLID MATTERS IN THE BLOOD 166 



the cells to the blood, and their presence indicates another function 

 of blood, viz., the removal of wastes. (See p. 352, Excretion.) 



Blood Salts. The mineral salts are probably absorbed in the 

 same way as the other nutrients, and their presence accounts for 

 the osmotic pressure of the blood as well as for the alkaline reaction. 

 This last is mainly due to the presence of the salt, sodium carbon- 

 ate. Certain proteids (notably the globulins) are kept in solution 

 by the presence of salts. 



Water of blood. — This liquid is taken in by osmosis from the 

 digestive tract and other parts of the body, and the liquid character 

 of blood is mainly due to it. It forms 78% of the entire blood. 



The solid matters in the blood. — Having now a general 

 idea as to the nature of the liquid plasma, let us turn to 

 the solid parts. We have already noted that blood con- 

 tains two kinds of corpuscles, the red and the white. In 

 addition to these solids, blood contains a third set of bodies 

 called blood plates. These three solids are only slightly 

 heavier than the plasma, and the movement of the blood 

 keeps them pretty thoroughly mixed with the plasma. A 

 knowledge of their origin and function is necessary to a 

 clear understanding of the blood functions. 



Red corpuscles. These bodies to which the red color 

 of the blood is due, are shown by the microscope to be 

 biconcave, circular disks which are usually banded to- 

 gether in rolls like a roll of coins. (See Fig. 58.) They are 

 very small, having an average diameter of about .0077 

 milUmeter, and while their number varies greatly with the 

 condition of health the average is five million to a cubic 

 millimeter of blood in males, and four million and a half 

 per cubic millimeters in females. When viewed singly 

 they are seen to be of a yellowish-red color, but in masses 

 they appear deep scarlet. This red color is due to a 

 pigment which they contain called haemoglobin. Hffimo- 



