iv Tin: i-.i.oon 3 i 



Composition of Plasma. 1'lasma differs from scrum 

 in containing in addition to albumin and globulin, a third 

 protrid which is (ailed fibrinogen. Fibrinogcn is very like 

 the globulin of scrum (serum globulin, or paraglobulin as it is 

 Miinrtiint -s tailed), but differs from it in being coagulated at a 

 lower temperature. It solidifies and turns white at 56 Centi- 

 grade (132 Fahrenheit), while the serum albumin and serum 

 globulin do not coagulate till the temperature is raised to about 

 75 C. (167 F.). Fibrinogen is the substance in the plasma 

 which changes into the solid fibrin during the clotting of the 

 blood. 



When the blood is shed, some of the colourless corpuscles 

 break up and discharge into the blood a peculiar substance 

 called fibrin ferment. The presence of a very little of this 

 substance so influences the fibrinogen as to make it able to 

 turn into fibrin. 



The Salts of the Blood. Salts are present in the 

 plasma and in the serum in small quantity, less than I in 100 

 parts. They are chiefly carbonates, chlorides, and phosphates 

 of sodium and potassium, with salts of calcium and magnesium 

 in smaller quantity. The blood is alkaline, due to the alka- 

 line salts it contains. 



During the clotting of the blood the fibrinogen probably 

 takes up some of the calcium of the plasma in becoming 

 turned into the new substance, the fibrin. 



Observation of the Circulation of the Blood 



The blood carries to the tissues all the nourishment which 

 these require. The cells of which the tissues consist get all 

 the material they require for the building up of their own sub- 

 stance and the oxygen they need for their life from the blood, 

 and give to the blood the waste substances and the carbonic 

 acid which they cast off. In order to bring to the tissues 

 a proper supply of food, the blood must pass through the 

 organs which receive the food the animal eats ; it must also 

 pass through the lungs to get oxygen from the air ; and in 

 order to get rid of the waste substances, it must pass through 

 the organs whose function it is to remove these. We thus see 

 the necessity for the circulation of the blood. 



