HISTOLOGY 55 



After stimulation of the splanchnic nerves, however, the me- 

 dulla alone appears to be chiefly affected. 183 



The cells of the adrenal cortex move towards the center to 

 replace the innermost cells near the medulla which are con- 

 stantly dying. Degenerative processes can be seen in many 

 cells of the normal reticular zone with mitosis in the outer por- 

 tion of the cortex 362 The process of degeneration can be ac- 

 centuated by a number of toxic agents — phenol, chloroform, 

 mustard gas, bacterial suspensions, metallic poisons, malnu- 

 trition, starvation, etc. — thus permitting the experimental 

 study of the regeneration of the destroyed tissue. The guinea 

 pig has been particularly useful in the study of these processes 

 for its adrenals are extremely sensitive to toxic agents. 301 As 

 von Behring showed in 1895, hyperemia and hemorrhage of 

 the adrenals of the guinea pig follow the injection of diphtheria 

 toxin before any other organ is affected. 



The reticular zone is the site of the normal degeneration of 

 the cortical cells and invariably suffers the most damage in 

 infectious or toxic processes. It is also the site of most marked 

 congestion, hemorrhages, focal degenerations, or other results 

 of injury. In older animals the area of degeneration is greater 

 and there is less evidence of mitotic activity than in young 

 individuals. 301 



The normal and pathologically induced degenerative changes 

 observed in the adrenal are repaired by mitotic activity, which 

 is found mainly in the outer portion of the fasciculata or in 

 the border level between the glomerulosa and fasciculata. 



The connective tissue of the adrenal also proliferates rapidly 

 after hemorrhage, trauma, or other severe injury. The nec- 

 rotic area becomes enveloped by connective tissue, the cellular 

 debris is gradually absorbed, and finally only a scar remains 

 at the site of injury. 



The removal of the constantly degenerating cells of the re- 

 ticularis is brought about by infiltrated polymorphonuclear 

 leucocytes in severe lesions and by macrophages, plasma cells, 



