286 PATHOLOGY OF NUTRITION. 



Fibrosis. 



In fibrosis, or fibroid substitution, there is a wasting of the 

 true parenchyma-cells and an increase in the connective tis- 

 sue. It is not, strictly speaking, a degeneration except in 

 that the new material is considered inferior to the original. 

 When the change takes place in the central nervous system 

 it is spoken of as a sclerosis ; in the liver and kidney, as cirrho- 

 sis. It is often regarded as an evidence of chronic inflamma- 

 tion, for we know that there often results a great increase 

 in the amount of connective tissue in an area so affected. But 

 the change often occurs where there has been no inflammation. 

 In pseudohypertrophic paralysis, which is not usually re- 

 garded as an inflammatory process, the true muscle-cells are 

 almost entirely atrophied, yet by reason of the increase in the 

 connective tissue the calves of the legs are greatly enlarged. 

 In fibroid heart and the various scleroses of the central 

 nervous system there is considerable doubt about the inflam- 

 matory nature of the change. In the liver and kidneys, how- 

 ever, it is undoubtedly a frequent sequel of long-continued 

 inflammations. 



TUMOES. 



Definition : A tumor is a non-inflammatory, circumscribed 

 swelling which has no function. 



Etiology : Though a great many theories have been ad- 

 vanced, we actually know but little as to the causation of 

 tumors. The older authors referred to a peculiar constitu- 

 tional dyscrasia in this connection. Yirchow laid great stress 

 upon some unusual irritant as the exciting cause, as, for in- 

 stance, cancer of the breast following a blow or other injury 

 to the part; or the development of an epithelioma of the 

 tongue at the site of chronic irritation produced, for instance, 

 by a jagged tooth. Cohnheim advanced the theory that " in 

 an early stage of embryonic development more cells are pro- 

 duced than are required for building up the part concerned, 

 so that there remains a certain number unappropriated, which, 

 owing to their embryonic character, are endowed with a 

 marked capacity for proliferation." Some irritant or injury 

 causes a flux of blood to the part and determines the multk 



