THE CELLULAR CHANGES OF AGE 75 



even when the death of the cells is normal and occurs 

 in the regular course of development, that the cause 

 of the cells' death is extraneous to them, not intrinsic. 

 The subject of the death and disintegration of cells 

 is an exceedingly complex one, and might well occupy 

 our attention for a long time. But it is not permis- 

 sible to depart from the strict theme which we have 

 before us, and I will content myself, therefore, with 

 throwing upon the screen two tables 1 which illustrate 



1 I. DEATH OF CELLS 

 First. Causes of death. 



A. External to the organism : 



(1) Physical (mechanical, chemical, thermal, etc.). 



(2) Parasites. 



B. Changes in intercellular substances (probably primarily due to cells) : 



(1) Hypertrophy. 



(2) Induration. 



(3) Calcification. 



(4) Amyloid degeneration (infiltration). 



C. Changes inherent in cells. 



Second. Morphological changes of dying cells. 



A. Direct death of cells : 



(1) Atrophy. 



(2) Disintegration and resorption. 



B. Indirect death of cells : 



(1) Necrobiosis (structural change precedes final death). 



(2) Hypertrophic degeneration (growth and structural change often 



with nuclear proliferation precede final death). 

 Third. Removal of cells. 



A. By mechanical means (sloughing or shedding). 



B. By chemical means (solution). 



C. By phagocytes. 



II. INDIRECT DEATH OF CELLS. 

 A. Necrobiosis. 



(i) Cytoplasmic changes : 



(a) Granulation. 



(b) Hyaline transformation. 



