78 VETERINARY STUDIES 



and capillaries. An organ so affected is apt to be bluish in 

 color, spongy, moist and cool. This condition may be due to 

 weakened heart action, or to obstruction in veins, and less fre- 

 quently to obstruction in arteries or capillaries. Some of the 

 local changes that may follow passive congestion are exudation 

 of serum (dropsy), abnormal development of connective tissue, 

 clots in the vessels, and local tissue death (necrosis). 



Anemia 



Definition. — Anemia is an abnormal condition characterized 

 by a deficiency of total volume or a deficiency of corpuscles. 

 Anemia due to deficiency may be either general or local. Dis- 

 turbances of the nerve fibers (vasomotors) which control the 

 involuntary muscle fibers of the blood vessels have the same 

 relation to anemia as to hyperemia. By contracting or relaxing, 

 the muscle fibers decrease or increase the size and therefore, the 

 holding capacity of the blood vessels. 



General anemia. — This refers to a state of ill health charac- 

 terized by general lack in total volume of blood or to a lack in 

 relative number of corpuscles. This may be caused by hemor- 

 rhage, poor nutrition, destruction of red cells, as by chemical 

 poisons or by bacterial toxins, or disorder of blood-forming 

 tissues. General anemia is seen in the horse disease known as 

 swamp fever, where the mucous membranes become pale, or in 

 a case of castration when the colt bleeds badly. 



Local anemia. — Local anemia may be due to : decreased inflow 

 or increased outflow ; for example, pressure upon the part ; con- 

 traction of arteries supplying this part; excessive blood else- 

 where in the body; cold or chemical agents. In such cases the 

 organ is pale, flabby and dry, and it does not bleed normally 

 when cut. 



Results. — Either anemia or passive congestion results in tis- 

 sue starvation, deprivation of oxygen and accumulation of waste, 

 and the seriousness depends upon extent, location and duration. 

 An anemia may be very serious in vital organs or much less 

 important in such organs as the skin and muscles. During 

 anemia, nutritive changes are restricted and the processes of 

 excretion are checked. Waste products therefore accumulate. 



Complete and persistent anemia results in death of the tissue 

 (necrosis). 



