INTRODUCTION. 2 1 



material^ which gives to the organ in which it occurs a 

 waxy character. The process generally commences in the 

 small vessels of the part. It has not been found, as yet, 

 to have much clinical importance. Special chemical, 

 microscopical, and physical tests enable us to determine 

 the presence of these changes in parts. These will be 

 found recorded in more special works. Fatty, calcareous, 

 and pigmentary changes, when sufficiently advanced to 

 produce serious disorder, can readily be detected by the 

 unaided senses of the observer. Let it be clearly under- 

 stood that all these degenerations and infiltrations are 

 physiological processes in excess or out of place; they 

 may also be deficient, as occurs in rachitis where there is 

 deficient deposition of lime in the bones. They result 

 from perverted states of nutrition, dependent upon con- 

 ditions of the blood or of the cell-elements themselves. 

 Certain forms of degeneration lead to increase in the size 

 of organs, and very considerable modification of form. 

 The tissues are so arranged as to form solid or hollow 

 organs. When the former are the seat of changes their 

 increase in size and change of form causes them to press 

 upon neighbouring parts, and thereby interfere with 

 functional duties ; or softening with rapid enlargement 

 may lead to rupture, as is sometimes seen in the liver. 

 It must be remembered that very considerable degeneration 

 of an organ may occur without alteration in bulk, increase 

 in size of some parts atoning for diminution of others, 

 and vice versa. Here we have a case of degeneration 

 with atrophy. When a hollow organ is involved in these 

 degenerative processes they may lead to thickening of its 

 walls with or without diminution of its cavity, or to 

 thinning of the walls — atrophy — a condition which, with 

 concomitant softening, tends to produce rupture. When 

 an organ is subjected to free supply of nourishment, with 

 high functional activity, it becomes hypertrophied, this 

 condition consisting of an increase in the number (hyper- 

 plasia) or size of active tissue elements ; such a change 

 must be carefully distinguished from other forms of enlarge- 

 ment. It occurs often as a provision against disease ; 



