268 PHYSIOLOGY CHAP. 



a gradual disintegration of the chromatic substance of Nissl's 

 granules (see Fig. 124, p. 189), which spreads uniformly over the 

 cell protoplasm. This process (known as chromatolysis) is accom- 

 panied by a swelling of the cell, with lateral displacement of the 

 nucleus, followed later by a diminution in the volume of the cell, 

 and the partial or total disappearance of the chromatic substance. 



In studying the cytological changes in the nerve-cell after 

 prolonged work, Lambert, Eegnat, and Mann saw that the nerve- 

 cell diminishes in size and that the chromatic substance is 

 disintegrated and gradually disappears, but Nissl, on repeating 

 these observations, obtained unconvincing results, though he 

 observed a certain diminution of the chromatic substance. 



Clearer and more definite results ensue on severing the axon 

 from the cell, as shown by the investigations commenced by Nissl, 

 and continued in particular by Lugaro, Marinesco, and Van 

 Gehuchten. The first signs of chromatolysis in the cell were 

 observed twenty-four to forty-eight hours after section of a 

 motor nerve. The chromatolytic process goes on for about fifteen 

 days, when the cell is reduced to a rounded mass destitute of 

 Nissl's granules. The chromatolysis begins near the point of exit 

 of the axis-cylinder, then invades the perinuclear portion of the 

 cell, next the more peripheral part, and lastly the dendrites. 

 After twenty to twenty-four days the process of regeneration sets 

 in; it progresses very slowly, and is complete in about three 

 months. 



Alterations in the sensory cells after section of the peripheral 

 nerve were studied by Lugaro, Fleming, Cox, and others. On 

 cutting the spinal root between the ganglion and the cord, Lugaro 

 found few signs of chromatolysis in the cells of the ganglia. Van 

 Gehuchten and 'Nelis, on the contrary, observed chromatolysis in 

 the cells of the jugular ganglion after section of the vagus. It 

 differed only in not being followed by a process of reintegration, so 

 that after about three months the cells had almost entirely dis- 

 appeared. Nissl noted the same result in certain motor cells also, 

 and Schafer in the cells of Clarke's column, after section of the 

 direct cerebellar tract. This ascending or retrograde degeneration 

 after section of the nerve is a valuable help in localising the centre 

 connected with given nerve paths (Gudden's method). 



It is easy to understand that all portions of the processes 

 separated from the nucleus degenerate, since the nucleus is the 

 centre of nutrition for the entire neurone : it is more difficult to 

 explain the cause of chromatolysis and the degeneration of the cell 

 body after the severance of a part of the axon. The disintegra- 

 tion and degeneration described by Van Gehuchten for certain 

 sensory cells are probably due to the loss of function, after inter- 

 ruption of the paths by which peripheral excitations normally 

 reach the cell. But this explanation is not applicable to the 



