70 PATHOLOGY. 



Physiological hypertrophy is illustrated in the blacksmith's 

 arm, where there is an enlargement due to an increased exercise 

 and therefore increased nutrition to the muscles. If one kidney 

 he removed, the other enlarges to compensate. 



Pathological hypertrophy is illustrated in fatty degeneration 

 of the heart, in which this organ undergoes fatty changes and 

 becomes larger, hut loses in strength and usefulness. 



In any hypertrophy the newly formed elements are more 

 nearly like the normal when the circulation is most vigorous. 



Atrophy is the opposite of hypertrophy and is characterized 

 by a 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 he due either to decrease in size 

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

 ments. 



Local atrophy may be caused by: (I ) decreased amount of 

 blood and decreased nutrition, (2) nerve disturbance which some- 

 times results in very rapid atrophy, (3) inflammation; (4) exces- 

 sive functional activity and exhaustion of the tissue elements; (5) 

 continuous pressure. 



General atrophy mav be caused by lack of nutrition or ex- 

 cessive consumption and wastages of the soft tissues, especially 

 the fats which are first taken ; e. g., in typhoid fever in the human, 

 or influenza in the horse. 



Degenerations and infiltrations are characterized by changes 

 in the quality of a tissue; the bulk may or mav not remain the 

 same. When tissue degenerates, cheaper material mav be de- 

 posited in and actuallv becomes a part of the tissue. This is 

 degeneration. When infiltration occurs, the lower grade tissue 

 is deposited between the fibers or tissue elements, whatever these 

 may be. The proper elements ma) - then shrink. The tissue or 

 organ loses in functional strength and activity in either case. 



fatly degeneration is characterized by a deposit of fatty mat- 

 ter into and as a part of the tissue elements, especiallv common 

 in muscular tissue. 



Fatty infiltration is characterized by a deposit of fatty mat- 

 ter between the elements according to the previous definition. 

 Either ma)- be caused by ( 1 ) deficiency of blood and consequent 



Digitized by Microsoft® 



