I2O 



ELEMENTARY PHYSIOLOGY 



In the body the bright scarlet blood is usually found in the 

 arteries (vessels which convey blood from the heart), while the 

 dark purple blood usually flows through the veins (vessels which 

 convey blood to the heart). Hence the bright blood is often 

 termed arterial, and the dark blood venous. 



When a drop of dark blood from a vein is left exposed to air, 

 it absorbs oxygen from the air, and soon becomes bright. This 

 change may also be illustrated as follows : 



Half fill a test-tube with dark venous blood, and shake it up with the air 

 contained in the tube. It will speedily turn to a bright scarlet ; but, if set 

 aside for some time, will gradually turn dark again. This experiment may be 

 varied by causing air or oxygen to bubble through a vessel containing venous 

 blood. 



The temperature of the blood is 98-4 F. in health, but is 

 not exactly the same in all parts of the body at the same time. 

 The high temperature is due to chemical action, chiefly the oxida- 

 tion of carbon and hydrogen of the tissues. The blood is warmed 

 as it passes through muscles, glands, and other active organs ; but 

 is cooled slightly in the capillaries of the skin. 



The quantity of blood in the body also varies with certain 

 conditions, but is usually estimated at about one-tenth the total 

 weight of the body. 



The following table shows the composition of human blood as 

 far as its proximate principles are concerned : 



Water 785-0 



Red corpuscles (dry) ..... 130-0 



Albumen (dissolved in the serum) . . . 70-0 



Fibrin (elements of) . . . . . . 2-2 



Fatty matter ....... I '4 



Common salt ....... 3 '6 



Other salts I '8 



Colouring matter, waste, and , g 



accidental matters, &c. > 



lOOO'O 



When blood has been dried by the evaporation of all its water, 

 its ultimate or elementary chemical composition is almost identical 

 with that of dried flesh. Under these circumstances the composi- 

 tion of blood is 



Carbon . . . . . . . .58-0 



Oxygen ........ 19^0 



Nitrogen . . . . . . . .17-5 



Hydrogen . . . . . . . .7' 



Ash (mineral matter) . . . . . .4*5 



Some of the uses of the blood have already been pointed out 

 in connection with certain organs, and others have yet to be 

 mentioned. The chief uses, however, may be summarized as 

 follows : 



i. It serves as a storehouse for nutrient matter absorbed 



