230 PRINCIPLES OF VETERINARY SCIENCE 



Passive hyperemia is an overfilling of the veins with blood. 

 The affected part becomes larger and bluish-red in color. In 

 most animals the color cannot be seen, as the skin is pigmented. 

 The "stocking" or filling of the legs is a form of passive conges- 

 tion. It may be prevented by hand-rubbing and applying band- 

 ages to the legs as soon as the horse returns from work. A 

 laxative diet should be provided for such animals. The swelling 

 which occurs along the belly of a mare a few days or weeks before 

 foaling is another example. It is due either to a compression 

 of the walls of the veins, so that blood cannot circulate freely 

 through them, or to weakened heart action. The large milk 

 veins of some cows are often in a state of passive congestion due 

 to a damming back of the blood into them. In such cases they 

 are not an index to the quantity of milk which the animal is 

 capable of producing. Long continued or sudden and complete 

 passive congestion causes the blood to stagnate and its watery 

 constituents to exude through the vessel walls into surrounding 

 tissues. 



Anemia is the opposite of hyperemia. In this condition there 

 is either a diminution in the quantity or quality of the blood or 

 both. It may be either general or local. 



General anemia is due to a deficiency in the total quantity of 

 the blood. It is caused by excessive hemorrhage, poor nutrition, 

 or anything which destroys the red blood-corpuscles, particularly 

 parasites. Animals suffering from general anemia are said to 

 have "thin blood," their mucous membranes are pallid, and they 

 are listless. 



Local anemia is that condition in which there is less blood in the 

 part than normally, but the total amount of blood in the body 

 is not reduced. It is brought about by (1) pressure on the part; 

 (2) a thickening in the wall of a blood-vessel; (3) partial occlusion 

 of the artery to the part; (4) cold and chemical agents; (5) conges- 

 tion of blood elsewhere in the body. The part affected feels 

 cooler and is paler than normal. If long continued, death of the 

 part takes place from lack of blood supply. 



Hydremia is an increase in the water content of the blood. 

 It is not a very common disease so needs but passing mention. 



Septicemia is a morbid process in which septic or poisonous 

 substances are present in the blood. When toxins only are 

 present, the condition is termed toxemia. In most cases bacteria 



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