SECTION X. 



THE CIRCULATION OF DIGESTED FOOD.' 



The Blood. — After the food is digested it is absorbed and 

 enters into the blood. The special functions of the blood are to 

 nourish all the tissues of the body, and thus aid their growth 

 and repair; to furnish material for the purpose of the body 

 secretions, to supply the organism with oxygen without which 

 life is impossible, and finally to convey from the tissues the 

 products of their activity. 



To enable all this to be carried out the blood is constantly in 

 circulation, is rapidly renewed, is instantaneously purified in the 

 lungs, and by means of certain channels it is placed directly in 

 communication with the nourishing fluid absorbed from the 

 intestines by which it is being constantly repaired. 



Physical Characters of the Blood. — ^The color of the blood 

 varies, depending upon whether it is drawn from an artery or a 

 vein ; in the former it is of bright scarlet color, while in the 

 latter it is purplish red. Blood examined under the microscope 

 is found to consist of an enormous number of red disk shaped 

 bodies termed corpiisdes floating in an almost clear liquid called 

 plasma. These corpuscles are both red and white; the former 

 are the more numerous and the latter the larger. These red 

 corpuscles contain a pigment called hcemoglobin which gives 

 blood its scarlet color. The scarlet or purplish color of the 

 blood depends upon the amount of oxygen with which the 

 haemoglobin is combined. When haemoglobin is charged with 

 oxygen it is called oxy-htzmoglobin. 



Arterial and Venous Blood. — Arterial blood contains more oxy- 

 gen and less carbonic acid than venous blood. The dark color 

 of venous blood is .not due to the greater amount of carbonic 

 acid it contains, but to the diminution of oxygen in the red blood 

 cells. 



Salts of the blood are divided between the plasma and the 

 corpuscles. Sodium chloride is the most abundant salt of the 

 blood, potassium chloride and sodium carbonate follow, and 



1 Adapted from Smith's Manual of Veterinary Physiology. 



