CHAPTER II. 



PATHOLOGY OF NUTRITION. 



ALL pathological processes are primarily nutritive ; but 

 the term is usually restricted to necrosis, the degenerations 

 and infiltrations, hypertrophy, atrophy, and tumors. 



Local Death. 



Necrosis is a local death of simple cells or groups of cells, 

 in contradistinction to general or somatic death. It is due to 

 mechanical, chemical, and thermic injuries ; interference with 

 the blood-supply ; and to lesions of the central nervous sys- 

 tem i. e., trophic disturbances. 



The mechanical causes of necrosis are numerous, such as 

 the crushing of a finger by violence. External pressure, as 

 from bandages or splints on bony prominences, may cause 

 necrosis, as may also tension, or pressure from within, pro- 

 duced by inflammatory exudates. It is often difficult to dis- 

 tinguish between the direct injurious effect of mechanical, 

 chemical, or thermic trauma on the tissue-cells and their 

 indirect effect through circulatory disturbances, as the blood 

 also undergoes changes resulting in coagulation and stasis in 

 the capillaries. A temperature of 50 to 68 C., if continued 

 for any length of time, causes necrosis and higher temperatures 

 more quickly. 



Obstruction of the circulation by a thrombus, embolus, or 

 atheroma of the vessel-walls produces necrosis. A number of 

 these causes may act together. If the vitality of a tissue has 

 been reduced by long-continued passive hypersemia, for exam- 

 ple as the result of uncompensated valvular disease of the heart, 

 it succumbs much more rapidly. A slight injury may suffice 

 in the aged or in conditions like typhoid fever, where the vital 

 forces are greatly depressed. In senile gangrene, to the 

 lowered vitality of the tissue are added a weak heart and 

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