218 THE CIRCULATORY APPARATUS 



of absorption by the process of digestion; and waste 

 products (urea, cholesterin, etc., resulting from the 

 breaking down of tissues following their functional 

 activities), which are carried to the kidneys, lungs, 

 and skin to be eliminated. 



Serum. Serum is a clear, transparent, straw-colored 

 fluid formed when blood coagulates or clots, due to 

 the contraction of the fibrin which separates after 

 several hours, following withdrawal or is found by 

 whipping the blood with twigs, upon which the fibrin 

 forms as whitish threads. The serum consists prac- 

 tically of the same substances as the plasma, excepting 

 the proteins which are found in the fibrin. 



Serum-albumin represents the protein constituents 

 of the blood found in the plasma. It is absorbed 

 from the digestive tract in the form of peptones which 

 are formed from the proteins in a manner not definitely 

 decided upon by physiologists. It replaces the proteins 

 which have been used up in the disintegration of tissues 

 (anabolism). 



Paraglobulin is supposed to be similar to serum- 

 albumin as regards its function, and can only be 

 isolated from the blood serum by chemical methods. 



Fibrinogen is found in the blood, plasma, lymph, peri- 

 cardial, and peritoneal fluids. It can only be studied 

 by treating blood by chemical means before coagulation. 

 Its importance in regard to its function and nutritive 

 values is an undetermined quantity, aside from the 

 fact that it contributes to the formation of fibrin. 



Fat is found in the serum as microscopic globules. 

 The amount is very small (0.25 per cent.); however, 

 after a hearty meal the quantity is increased. 



Sugar is present in the form of dextrose, which is 

 a member of the carbohydrate group of body con- 

 stituents derived from fruits, cereals, etc., taken as 

 foods. 



Extractives include the nitrogenized bodies, urea, 

 uric acid, creatin, xanthin, etc., various chemical com- 



