CHAPTER II. 



ATROPHY, DEGENERATION, PIGMENTATION, AND 

 NECROSIS. 



General Considerations. 



THERE are three phases of activity in the transformations of energy 

 which are characteristic of living cells. These are nutrition, reproduc- 

 tion, and functional activity. But while these manifestations of energy 

 are more or less distinct as properties of living matter, they are closely 

 interdependent. It is the suitable balance of these activities fixed by a 

 prolonged environment which determines what we call health. When 

 this balance is disturbed beyond the limits of physiological variation, the 

 alterations which result may be manifest, either in the diminution or de- 

 struction of tissue, or in its increase or new formation. In other words, 

 the cells of the body when placed under conditions which seriously in- 

 terfere with the orderly transformations of energy may undergo altera- 

 tions from the normal which are retrogressive on the one hand, or pro- 

 gressive on the other. 



It is well to remember that retrogressive as well as progressive 

 changes in the body are not limited to pathological conditions but form 

 a part of the normal processes through which growth is secured and 

 function maintained. ' 



"We shall in this chapter consider the retrogressive processes and their 

 effects ; in the next those which are progressive. 



Atrophy. 



Atrophy is a diminution in the size of the body, of organs, or of tissue 

 elements. It occurs as a physiological process in man as well as in cer- 

 tain of the lower animals. Thus in man the t.hymus and the umbilical 

 vessels undergo atrophy at an early period ; while in old age atrophy of 

 the sexual organs and of the tissues in general is the usual mark of senil- 

 ity. 2 On the other hand, as a pathological process, atrophy may occur 

 in connection with disturbances of innervation or nutrition ; from disuse 

 or from pressure ; or from the presence of poisons. Although it is con- 

 venient to name these as phases of atrophy, they are not fundamentally 



1 For a resume of the relationship between normal and pathological retrogressive 

 processes see Minot, Middleton Goldsmith Lecture on "The Embryological Basis of 

 Pathology," Science, March 29th, 1901. 



2 For a study of the changes in the body in development and senility see the mono- 

 graph of Muhlmann, Wiesbaden, 1900, Bibl. 



