CH. xvil.] NISSL'S GRANULES. 2OF 



and in extreme cases extrusion of the nucleus. High fever 

 (hyperpyrexia) causes a very similar change, which is doubtless 

 associated with the coagulation of the proteids of the cell- 

 protoplasm by the high temperature. 



Since attention has been directed towards the Nissl granules, a 

 literature which has become alarmingly vast during the last few 

 years has sprung up in relation to them. This is quite easy to 

 understand, for neurologists have by this sensitive test been able 

 to identify changes in the cells which could not be detected by the 

 previous methods of staining. Thus the cells have been examined 

 in various diseases, and after being subjected to the action of 

 various poisons. In a new subject of this kind there is, as would 

 be expected, considerable divergence of views, and even the 

 fundamental qxiestion has not yet been answered satisfactorily 

 whether the Nissl granules are present as such in the living cell, 

 or whether they are artifacts produced by the fixative action of 

 strong alcohol The fact that they cannot be demonstrated when 

 the cells are stained by the injection of methylene blue into the 

 circulation before the animal is killed is a very strong piece of 

 evidence in favour of the latter view. But, whichever view is 

 correct, the method is a valuable one, and Nissl's views on this 

 question appear to be indisputable : they are briefly as follows : 

 Healthy cells fixed and stained in a constant manner will appear 

 the same under constant optical conditions, and the appearances 

 thtn seen form the equivalent of such healthy cells during life. 

 It follows that if the cells prepared by the same method and 

 examined under the same conditions show a difference from the 

 equivalent or symbol of healthy cells, the difference is the measure 

 of some change that has occurred during life. 



Chromatolysis is the term applied to designate the disappearance 

 or disintegration of the Nissl gramiles. The process generally 

 begins at the periphery of the cell and in the dcndrons, but in 

 advanced cases the whole cell may be affected. We have already 

 alluded to the fact that chromatolysis occurs in various abnormal 

 states, and the diminution of the chromophilic nucleo-proteid 

 indicates a diminution of the vital interaction of the highly 

 phosphorised nucleus with the surrounding cell protoplasm. 

 Chromatolysis alone is not indicative of cell destruction, and a 

 cell may recover its function afterwards. The integrity of the 

 nucleus and of the fibrils appears to be much more important to 

 the actual vitality of the cell. 



When a nerve-fibre is cut across, the distal segment undergoes 

 Wiillcrian degeneration ; this is an acute change. But the nerve- 

 cell and the piece of the nerve-fibre still attached to it do not 



