THE NERVOUS SYSTEM. 805 



ferent poisons and in different types of neurones. The effects of the 

 same poison upon a given type of neurone also vary according to its 

 rapidity of action, whether rapidly fatal or extending over a considerable 

 period of time. Again, given the same poison and the same time of 

 action, not all neurones even of the same type show an equal suscepti- 

 bility. There seem to be marked individual differences among neurones 

 of the same type as regards their resisting powers. 



These changes in the neurone from the action of toxins may affect one 

 or all of its structural elements, and vary from the slightest appreciable 

 loss of staining qualities of the chromophilic bodies to complete destruc- 

 tion of the neurone. In the chromophilic bodies the essential change 

 seems to be a decrease in the amount of chromatic substance, chromatol- 

 ysis. This may be evidenced merely by a decreased staining intensity, 

 the chromatic masses appearing abnormally pale ; the bodies may have a 

 ragged or frayed-out appearance at their edges ; they may be shrunken, 

 or, retaining their normal shape and size, become vacuolated (Plate 

 XIII., 3) ; they may completely disintegrate, giving to the cell a diffuse 

 granular appearance ; they may disappear, leaving the cell entirely devoid 

 of chromatic substance. The chromatic masses in the deudrites seem in 

 many cases to be more resistant or less exposed than are those in the body 

 of the cell, often remaining unchanged at a time when the latter show an 

 advanced degree of chromatolysis. During these changes in the chro- 

 matic element the cyto-reticulum may remain apparently normal or it 

 may more or less completely disintegrate. This disintegration usually 

 marks the more advanced degenerative changes (Plate XIII. , 4). 



In the truly achromatic element of the cell or cytoplasm, our present 

 methods of staining fail to demonstrate lesions. Diffuse staining of this 

 basement substance is a common phenomenon of chromatolysis, but seems 

 more properly referable to a diffusion of the fine granules resulting from 

 disintegration of the chromatic masses than to any change in the cyto- 

 plasm itself. Disappearance of the formed elements of the cell often 

 leaves clear holes or vacuoles in the cell body or gives the appearance of 

 cracks or fissures. The nucleus may remain normal ; it may swell and 

 its contour become abnormally distinct ; it often takes a diffuse stain ; 

 later it shrinks, becomes crenated, its reticulum and limiting membrane 

 break up and its outline is lost. During these nuclear changes the nu- 

 cleolus may also disintegrate. It is often extremely resistant, remaining 

 apparently unchanged after most of the other parts of the cell have be- 

 come unrecognizable. Concurrent with these changes in internal struc- 

 ture are changes in the shape and size of the cell. Its contour becomes 

 irregular, and its edges present an eroded appearance; the cell body 

 shrinks away from its cell space, breaks up, and ultimately disappears. 

 The dendrites undergo alterations similar to those in the body of the cell. 

 They shrink, become separated from the cell body, and finally disinte- 

 grate. 



That part of the neurone which shows most marked evidences of its 

 effect is not necessarily the part upon which the poison is most directly 



