PROGRESSIVE TISSUE CHANGES. 189 



the tissues of a hollow organ, accompanied by a diminution in 

 the lumen of the holluw organ, e. g., hypertrophy of the heart, 

 oesophagus, intestine, or any other hollow organ in which the 

 hypertrophied tissues occupy a portion and tlius diminish the 

 lumen of the organ. 



In some instances hypertrophy represents a normal, physio- 

 logic process. Tlie increased size of the pregnant uterus, and 

 the enlargement of the mammae during the gestation period are 

 examples of physiologic hypertrophy. Increased size of the 

 heart and voluntary muscles in horses trained for racing rep- 

 resents a physiologic h_\'pertrophy. After the destruction of one 

 kidney b}- disease or the removal of one by operation, the re- 

 maining kidnev increases in size and ultimately performs tlic 

 function of both, this is functional or physiologic hypertropliy 

 and also compensatory hypertniphy. In fact practically all hy- 

 pertrophies are physiologic, however, the hypertrophied struc- 

 tures are a1:)normal, therefrirc the condition is patliologic. 



Excessive development of an entire animal i. e., giantism is 

 designated by some as general hypertrophy. 



Excessive development of a part as one foot is designated 

 local h\'pcrtropliA-. Local livpcrtrr)pliy is nuich more common 

 than general li_\'pertri.ipliy. 



Hypertrophy may lie inlierited, (natural) or acquired. Ac- 

 quired h}'pertrophy may be antenatal or postnatal. 



Etiology. 



IxHERtTED iiypi-:rtr(:)PHV. — The cause of inlierited hypertrophy 

 i^ unknown except that there is an inherited impulse to grow 

 large. This type of hypertro])liy is noted in giants. 



AxTEX.\T.-\r, iiYPERTROPiiv is usuallv the result of unequal pres- 

 sure and amniotic adhesions. 



The causative f,\c'I'ors oe posTiX.vt.vl iivpI'RTROpiiy are, 1st. in- 

 creased nutrition, 2nd, increased function, :]d, a stimulus, prob- 

 al)ly an internal secretion, that causes the affected tissue to con- 

 sume excessive quantities of food. Two or more of these etio- 

 logic factors are usually evident in all cases of hypertrophy. 



Increased nutrition.— A long continued, mild arterial hypere- 

 mia in a tissue insures increase of the nutritive supply to the 

 aft'ected part and such parts usually l)ecome hypertrophic. 



Increased function is the prime causative factor of physiologic 

 or functional hypertrophy. Increased function is intimately 

 associated with increased nutrition, in fact long continued in- 

 creased function without increased nutrition is not possible. In 

 the production of functional hypertrophy the part must be 



