70 PATHOLOGY. 



Physiological hypertrophy is illustrated in the blacksmith's 

 ^rm, where there is an enlargement 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 fatty degeneration 

 •of the heart, in which this organ imdergoes fatty changes and 

 becomes larger, but loses in strength and usefulness. 



In any hypertrophy the newly formed elements are more 

 aiearly 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 be 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 may 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 may not remain the 

 ■same. When tissue degenerates, cheaper material may be de- 

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

 ■■degeneration. \\'hcn infiltration occurs, the lower grade tissue 

 is deposited between the fibers or tissue elements, whatever these 

 may be. The proper elements may then shrink. The tissue or 

 • organ loses in functional strength and activity in either case. 



Fatty degeneration is characterized by a deposit of fatty mat- 

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

 in muscular tissue. 



Fatty infiltration is characterized by a deposit of fatty mat- 

 ier between the elements according to the previous definition. 

 Hither may be caused by ( i ) deficiency of blood and consequent 



