310 RETROGRESSIVE CHANGES 



body. This may be due to either or both of two factors : l 

 First, autolysis is much slower in alkaline than in acid media ; 

 outside the body autolyzing tissues develop an acid reaction 

 which favors their autolysis ; within the body this is checked 

 by the alkaline plasma. Second, the plasma contains autolysis- 

 inhibitiug substances, which also may interfere with self-diges- 

 tion in the body. In corroboration of the above may be 

 recalled the fact that large necrotic areas show autolysis first in 

 the center, where the alkaline, antagonistic body fluids pre- 

 sumably cause the least effect. Furthermore, it has been found 

 by Wells 2 that the histological changes of autolysis proceed 

 much faster in serum that has been heated to destroy the anti- 

 bodies than in unheated serum. Leucocytes, as Opie has shown, 

 contain autolytic enzymes acting best in an alkaline medium, 

 hence they perform their digestive function readily at the 

 periphery of necrotic areas. 



When a cell dies, certain physical changes occur that are 

 probably of considerable importance. The permeability of 

 the cell wall is almost immediately increased, so that all diffusible 

 substances readily pass through, i. e. y its semiperm cable character 

 is lost. This we see particularly in plant cells, which lose their 

 turgor with their semipermeability, and therefore the plant 

 wilts. Galeotti 3 has studied the changes in cells that occur 

 with their death, and finds that the electrical conductivity 

 decreases considerably at the time of death, while the molecular 

 concentration remains quite the same. This indicates that the 

 number of free ions is diminished, while the number of osmoti- 

 cally active molecules remains constant ; which Galeotti inter- 

 prets as meaning that living protoplasm is characterized by a 

 high degree of ionization. When secondary disintegrative 

 changes occur in the protoplasm, with the formation of many 

 small molecules from the large molecules of the cell, both 

 osmotic pressure and electrical conductivity increase rapidly. 



CAUSES OF NECROSIS 



Anemia. After the cutting off of blood-supply, cells soon 

 undergo morphological changes that we recognize as indi- 

 cating their death, and after a time they also become incapable 

 of returning to their normal condition when the blood-supply is 

 re-established, probably because of these structural changes. 



1 Literature and more complete discussion under "Autolysis." 



2 Jour. Med. Research, 1906 (15), 149. 



3 Zeit. f. Biol, 1903 (45), 65. 



