274 VKI'KRINARY PATHOLOGY. 



flaiiimation, degeneration, etc. Tissue resistance to the devel- 

 opment of neoplasms varies in diilerent animals, in the same 

 animal at different times, and possibly also in the different tis- 

 sues of the same animal. The resistance of the surrounding 

 tissue is made evident in some cases by the formation of a fibrous 

 wall iir capsule that limits and separates the tumor and the nor- 

 mal tissue. Degeneration and necrosis may also be interpreted 

 to be a result of opposed action by the invaded tissue. 



Retrogressive Changes. — Tumors are subject to the same 

 dep-enerative processes that normal tissues are. Hemorrhages, 

 necrdsis and degenerations are frequent m tumors because 

 of the imperfectlv furmed and irregular distribution of the 

 supplying vessels. The results of hemorrhage into tumors 

 depend upon the amount of extravasted blood and the secondary 

 changes therein. A tumor the size of a cocoanut would likely 

 become necrotic if a vessel ruptured and a half a liter of blood 

 escaped into the tumor tissue. A small quantity of extravasate 

 when infected with putrefactive microorganisms as a rule results 

 in necrosis of the tumor tissue. Necrosis is a sequel of ob- 

 structed circulation or results from the solvent action of meta- 

 bolic products. Thus, necrosis may be the result of thrombosis 

 or embolism. Thrombic formation is especially prevalent be- 

 cause of the irregularities of the lining of the tumor vessels. 

 Emboli are cummcin, as the^- are frecpiently detached tumor cells. 

 Circulation mav also be interfered with by pressure of the tumor 

 tissues, thus dbstructing the efferent or aft'erent blood vessels. 

 Some metabolic products of tumors constantly dissolve the sur- 

 face cells, resulting in ulceration, a common necrotic condition 

 observed in tumors. Tumors may be invaded with pyogenic 

 bacteria, resulting in suppuration. 



Of the degenerations, mucoid and colloid are the most com- 

 mon. Fattv degeneration and calcareous infiltration occur less 

 fre()uently. Mucoid degeneration aft'ects connective tissue and 

 epithelial tissue tumors, occurring more frequently in the former. 

 Colloid degeneration is found in epithelial tissue tumors. 



A four-kilogram (D-lb.) renal hypernephroma undergoing 

 collf)id degeneration was obtained on post-mortem examination 

 of a three-year-old steer. Fatty degeneration usually succeeds 

 necrosis in tumor tissue. Calcification of tumors is quite com- 

 mon. Pigmentation is more common in tumors than in normal 

 tissue. ]\Ielanomata are tumors containing melanin thsJt has 

 been deposited in the tumor cells. Chloromata are tumors con- 

 taining a green pigment. Hemoglobin, hematoidin and hemo- 



