84 VETERINARY STUDIES 



may be due to local, mechanical obstruction in the veins or lym- 

 phatic vessels, producing- sluggish circulation, as in the ' ' stock- 

 ing" of the horse's hind leg. 



Hypertrophy. — The term "hypertrophy" is applied to any 

 enlargement of any part or organ of the body. It may be due 

 to either an increase in the number of elements, or to an increase 

 in the size of existing elements, or to a combination of these 

 two conditions. Hypertrophy may be either physiological, 

 healthy, or pathological, diseased. The cause may be : continued . 

 increase of nutrition in a mild active hypermia, or moderately 

 increased use as in a muscle, or the presence of unknown factors 

 probably internal secretions, such as an enlargement of the mam- 

 mary gland in pregnancy. 



Physiological hypertrophy is illustrated in the blacksmith's 

 arm, where there is enlargement of muscles due to an increased 

 exercise and, therefore, increased nutrition to the muscles. If 

 one kidney be removed, the other enlarges to compensate. 



Pathological hypertrophy is illustrated in "elephant leg" 

 (lymphangitis) of horses, a condition in which the connective 

 tissue of the skin and underlying parts increases in quantity, 

 resulting in general enlargement of the leg. 



In any hypertrophy the newly formed elements are more, 

 nearly like the normal when the circulation is most vigorous. 



Atrophy. — This is the opposite of hypertrophy and is charac- 

 terized by decrease in bulk and weight, as, for instance, sweeny 

 of the shoulder muscles in horses. Atrophy may be general or 

 local, and the decrease in size may be due either to decrease 

 in size or number, or to decrease both in size and number of the 

 elements. 



The seriousness of this depends upon its extent and the part 

 involved. Atrophy of a nerve trunk means paralysis of func- 

 tion. Atrophy of a shoulder may not be very serious, and the 

 part may easily recover. 



Local atrophy, e.g., contracted hoof, or shoulder sweeny, may 

 be caused by: decrease in amount of blood and nutrition; 

 a nerve disturbance, which sometimes results in very rapid 

 atrophy; inflammation interfering with circulation and nutri- 

 tion ; insufficient activity or excessive activity and exhaustion 

 of the tissue elements which are thus worn out faster than they 

 are rebuilt; continuous pressure resulting in anemia and local 

 starvation. 



