ATROPHY AND DEGENERATIONS OF TISSUE. 59 



arteries, the walls of the heart, and the cartilaginous basis of 

 bones. 



Causes of fatty degeneration. — All influences which interfere 

 with the nutrition of a part may cause this change. Indeed 

 fatty degeneration may be looked upon as an advanced stage 

 of atrophy, and depending upon tlie same causes — namely, 

 diminished supply of blood, inflammation, decreased functional 

 activity, and diminished nervous influence. Eapid growth is 

 also a cause of degeneration of a part. Thus a rapidly growing 

 tumour is liable to softening and degeneration, as seen in the 

 softening of the central portions of cancer, &c.; and lastly, old 

 age, by impairing the vital activity, may cause degenerations 

 and softening of various parts of the economy. 



The formation of the fat depends upon changes in the tissue 

 itself, and not upon the deposit of it from without ; that is to 

 say, upon a conversion of the albuminous constituents of the 

 tissue into fat, in a manner similar to that process which occurs 

 after death, when from spontaneous decomposition a peculiar 

 kind of fat, named adipocere, is formed out of the albumi- 

 noid tissues. 



The fatty metamorphosis may be looked upon as a salutary 

 change when it occurs in new formations, in thrombi, and in 

 inflammatory exudates. Indeed it is only through the occur- 

 rence of this change that they are rendered liquid and capable 

 of absorption. 



Various changes may take place in the fatty degenerated 

 material. Sometimes it gradually dries up into a yellow substance 

 resembling cheese. This process is termed caseation, and appears to 

 be owing to a natural dryness of the tissue, and is most frequent 

 in parts which are not very vascular, or in those where the 

 vessels are occluded. This process of caseation is most frequently 

 seen to take place in new formations, composed of closely 

 crowded cellular elements, such as tubercle, growths in the lym- 

 phatic glands, &c. ; and in them the material, after gradually 

 drying up, may become enveloped in a capsule of fibrous tissue, 

 and remain inert in the midst of surrounding structures. These 

 cheesy matters are often met with, particularly in horned cattle, 

 in the lungs, pleura, and peritoneum, and are apt to cause consi- 

 derable confusion, as it has been the custom to look upon all 

 cheesy matter as tubercular. To conclude that these cheesy masses 



