30 THE VITAL PROCESSES 



fats, and salts (Chapter IX). Three kinds of proteids 

 are found in the plasma, called serum albumin, scrum 

 globulin, and fibrinogen. These resemble, in a general 

 way, the white of raw egg, but differ from each other in the 

 readiness with which they coagulate. Fibrinogen coagu- 

 lates more readily than the others and is the only one that 

 changes in the ordinary coagulation of the blood. The 

 others remain dissolved during this process, but are coagu- 

 lated by chemical agents and by heat. While all of the 

 proteids probably serve as food for the cells, the fibrino- 

 gen, in addition, is a necessary factor in the coagulation of 

 the blood (page 31). 



The only representative of the carbohydrates in the 

 plasma is dextrose. This is a variety of sugar, being de- 

 rived from starch and the different sugars that are eaten. 

 The fat in the plasma is in minute quantities and appears 

 as fine droplets the form in which it is found in milk. 

 While several mineral salts are present in small quantities 

 in the plasma, sodium chloride, or common salt, is the 

 only one found in any considerable amount. The mineral 

 salts serve various purposes, one of which is to cause the 

 proteids to dissolve in the plasma. 



2. The wastes are formed at the cells, whence they are 

 passed by the lymph into the blood plasma. They are car- 

 ried by the blood until removed by the organs of excretion. 

 The two waste products found in greatest abundance in 

 the plasma are carbon dioxide and urea. 



The substances dissolved in the plasma form about 10 

 per cent of the whole amount. The remaining 90 per 

 cent is water. Practically all the constituents of the 

 plasma, except the wastes, enter the blood from the digest- 

 ive organs. 



Purposes of Water in the Blood. Not only is water the 



