192 



Virjia^I NARY PA'l I ! OLOG Y . 



Interstitial liyl^crplasia is quite common as it is usually evi- 

 dent in chronic inflammatory tissues and it is also occasionally 

 observed in structures affected with functional fibrosis as is evi- 

 dent in the liver of animals afflicted with disturbances of the 

 cardiac valves. 



Etiology. 



The cause of parenchymatous hyperplasia is unknown. Inter- 

 stitial hvperplasia is produced by the lono^ continued action of 

 mild irritants or other substances that produce over stimulation. 



Appearance. 



Macroscopic. — rarenchymatous hyperplastic structures are 

 recrularlv or irreq-ularlv enlarged and are heavier than normal. 



Fig-. lO'i. — Pi-ii dra\\-ing uT an H.vperplawtic L'reter, ox, natural size 



Interstitial hyperplastic parts vary in appearance according 

 to the -amount of hyperplastic fibrous tissue. The part may vary 

 from normal to dense, hard, pale irregularly lobulated masses of 

 fibrous tissue. 



Microscopic. — Parenchymatous hyperplastic structures have 

 the same appearance microscopicallv as sections of normal tissue. 



Sections of tissue affected with interstitial hyperplasia con- 

 tain an increased r|uantity of fibrous tissue which may be readily 



