20 REPORT— 1900. 



characters which imply different structures. One stains deeply oti the 

 addition of certain dyes, and is named chromophile or chromatic sub- 

 stance ; the other, which does not possess a similar property, is the 

 achromatic network. The chromophile is found in the cell body and 

 the dendritic processes, but not in the axon. It occurs in the foi'm 

 of granular particles, which may be scattered throughout the plasm, or 

 aggregated into little heaps which are elongated or fusiform in shape 

 and appear as distinct coloured particles or masses. The achromatic 

 network is found in the cell body and the dendrites, and is continued 

 also into the axon, where it forms the axial cylinder of the nerve fibre. 

 It consists apparently of delicate threads or fibrillaj, in the meshes of 

 which a homogeneous material, such as is found in cell plasm generally, 

 is contained. In the nerve cells, as in other cells, the plasm is without 

 doubt concerned in the process of cell nutrition. The achromatic fibrillaj 

 exercise an important influence on the axon or nerve fibre with which they 

 are continuous, and probably they conduct the nerve impulses which 

 manifest themselves in the form of nerve energy. The dendritic processes 

 of a multipolar nerve cell ramify in close relation with similar processes 

 branching from other cells in the same group. The collaterals and the 

 free end of the axon fibre process branch and ramify in association with 

 the body of a nerve cell or of its dendrites. We cannot say that these 

 parts are directly continuous with each other to form an intercellular 

 network, but they are apparently in apposition, and through contact exer- 

 cise influence one on the other in the transmission of nerve impulses. 



There is evidence to show that in the nerve cell the nucleus, as well 

 as the cell plasm, is an effective agent in nutrition. When the cell is 

 functionally active, both the cell body and the nucleus increase in size 

 ( Vas, G. Mann, Lugaro) ; on the other hand, when nerve cells are fatigued 

 through excessive use, the nucleus decreases in size and shrivels ; the cell 

 plasm also shrinks, and its coloured or chromophile constituent becomes 

 diminished in quantity, as if it had been consumed during the jjrolonged 

 use of the cell (Hodge, Maun, Lugaro). It is interesting also to note that 

 in hibernating animals in the winter season, when their functional activity 

 is reduced to a minimum, the chromophile in the plasm of the nerve cells 

 is much smaller in amount than when the animal is leading an active life 

 in the spring and summer (G. Levi). 



When a nerve cell has attained its normal size it does not seem to be 

 capable of reproducing new cells in its substance by a process of karyo- 

 kinesis, such as takes place when young cells arise in the egg and in the 

 tissues generally. It would appear that nerve cells are so highly special- 

 ised in their association with the evolution of nerve energy, that they 

 have ceased to have the power of reproducing their kind, and the 

 metabolic changes both in cell plasm and nucleus are needed to enable 

 them to discharge their very peculiar function. Hence it follows that 

 when a portion of the brain or other nerve-centre is destroyed, the 



