CERTAIN DEVITALISED TISSUES. 247 



generation and decay; or, in other words, the 

 general laws of matter, which had previously been 

 suspended by the superior powers of life, once more 

 come into operation, and give rise to definite chemical 

 and physical changes. When the dead or decaying 

 tissues communicate freely with the atmosphere, as 

 in the different forms of gangrene, we at once recog- 

 nise various well-known physico-chemical changes as 

 the ordinary effects of the general laws of matter 

 acting on animal substances subjected to certain 

 conditions. But in the case of tissues not exposed 

 to the air, comprising the various internal organs of 

 the body, other and more gradual changes result 

 from a complete or partial deprivation of their 

 vitality. 



The most frequent of these changes are softening, 

 contraction or diminished bulk, induration, fatty 

 degeneration, and calcareous degeneration; all of 

 which morbid conditions are directly or indirectly 

 connected with the diminution or cessation of the 

 vital process of nutrition in the affected structures. 

 The defective nutrition inducing these changes may 

 either occur directly, as from old age, or an enfeebled 

 or diseased condition of the organs of circulation, or 

 as the result of local injury or disease, impairing or 

 destroying the inherent vitality of the degenerated 

 tissues, or it may be induced indirectly or as a secon- 

 dary effect of previous local inflammation or congestion. 

 For the nutrition of a part is necessarily dependent 

 upon the proper circulation of the blood through its 

 capillaries ; whereas in inflammation and congestion, 

 the motion of the blood through the nutrient vessels is 



u 4 



