164 



BLOOD AND LYMPH 



While our experiments show in a general way the com- 

 position of the blood, we must go to the chemist for a care- 

 ful analysis of its structure. Such chemical analyses show 

 the plasma to be composed of the following substances : 



Plasma 



COMPOSITION OF PLASMA. 



' Water . f Fibrinogen 

 Proteids . < Paraglobulin (serum globulin) 

 L Serum albumin 



[Fats 



Extractives j Ure^^ 

 [ Acids 



Salts . 



r Chlorides 

 I Carbonates 

 ■^ Sulphates , 

 Phosphates j 



^of 



Sodium 



Potassium 



Calcium 



Magnesium 



Iron 



_ Enzymes and unknown substances 



Blood proteids. — Fibrinogen is fibrin in the liquid state. It is, 

 of course, absent in the serum. It varies in amount from .22% to 

 .40% in human blood, and to it is due the clotting power of the 

 blood. (The causes of clotting will be discussed under a separate 

 heading, see p. 169.) 



Serum albumin is the form of proteid which is supposed to have 

 been formed from the digested proteids of the food. It forms 4.. 5% 

 of the blood of man, and is supposed to be the form of proteid used 

 in supplying the tissue cells. 



Paraglobulin forms 3.1% of the blood of man. Its origin and 

 function are at present unknown. 



The two proteids, then, whose functions are definitely known 

 are serum, albumin, and fibrin. 



Blood extractives. — The fats and sugars are ex'identl}' absorbed 

 from the digestive fluids, and as nutrients are carried to the tissues 

 for use as energy producers. 



Urea and acids are merely forms of waste matter given ofl by 



