CIRCULATION 19 



therefore, a convenient point of departure in beginning 

 the study of physiology. 



The blood consists of a liquid, plasma, and solid bodies, 

 red corpuscles, or erytlirocytes, blood platelets; and 

 white corpuscles, which are of two kinds, leucocytes and 

 lymphocytes. 



The plasma is all of the liquid part of the blood as it 

 exists in the living animal and is to be distinguished from 

 " serum, " which is the liquid part after coagulation Jias 

 occurred. Plasma consists chiefly of water, but contains 

 other substances of the greatest importance. The inor- 

 ganic salts, such as sodium chloride, calcium chloride, 

 and potassium chloride, as well as compounds of these 

 bases with other acid radicals, are of importance in re- 

 gard to the phenomena of osmosis, as influencing the ir- 

 ritability of muscle and nerve, and are supposed to play 

 an important role in the maintenance of the heart beat. 

 Calcium salts cause an increased vigor of contraction 

 and if present alone, cause the heart to stop tightly con- 

 tracted; while the salts of potassium tend to cause re- 

 laxation. It is suggested that the presence of these 

 salts in proper concentrations causes the alternate con- 

 traction and relaxation of the heart during life. 



Among the organic constituents are proteins, which 

 are known as fibrinogen, serum albumin, and serum glob- 

 ulin or paraglobulin. In addition, there are what may be 

 designated as temporary constituents of the plasma, sub- 

 stances on their way from the digestive canal to the tissues, 

 such as fat, sugar, the results of protein digestion; as well 

 as waste products on their way to the organs of excre- 

 tion; bodies known as hormones, which are produced 

 at one part of the body and sent elsewhere to influence 

 other structures; substances which are manufactured to 

 enable the animal to overcome bacterial invasion; and 



