THE PHYSIOLOGICAL CHEMISTRY OF THE NEURON. 553 



plasm and endoplasm there can be made out in tissues which 

 have been fixed a more or less homogeneous ground-substance 

 in which are deposited larger and smaller masses of a gran- 

 ular nature. The ground-substance corresponds in tissues 

 fixed with alcohol and stained by the methods of Nissl and Held 

 to the 'unstainable substance 7 of Nissl, and the masses of gran- 

 ules to the 'stainable substance 7 of Nissl and the pigment. 



"The 'stainable substance' of Nissl in healthy animals of 

 the same age and species, with the same method of fixing and 

 staining, is tolerably constant in appearance and arrangement 

 in the cell-bodies and dendrites of the same group of nerve- 

 cells: a fact of extreme importance for nerve-anatomy and 

 pathology. The axons appear to be entirely devoid of the 

 'stainable substance' of Nissl. Whether the stainable sub- 

 stances represent bodies precipitated from solution through the 

 action of reagents or bodies pre-exist ent, though invisible, first 

 brought into view through the action of fixing or staining re- 

 agents in the hardened tissues, in either case they appear to 

 yield the chemical tests characteristic of the group of nucleo- 

 albumins. Whether the staining reaction characteristic of the 

 stainable substance depends upon chemical relations or upon 

 purely physical conditions must, for the present, remain un- 

 decided. 



"The 'unstainable portion 7 of the cell-body, that is, the 

 ground-substance, though probably functionally much more 

 important than the stainable, is not so well understood; its 

 nature and structure are still as obscure as those of protoplasm 

 in general." Still, the link with features previously brought 

 out by our analysis now seems within reach. 



Held has maintained that the stainable Nissl bodies repre- 

 sent simply substances precipitated from solution by the action 

 of fixing mixtures; Fischer was led to the same conclusion. 

 Barker says, in this connection, that he repeatedly convinced 

 himself of the homogeneous appearance of the protoplasm of the 

 nerve-cell when it is examined immediately after the removal 

 from the living body. That the ground-substance is homo- 

 geneous, and that the unstainable portion is a product of dis- 

 sociation of some of its constituents, are therefore probable. 

 But the stainable portion we have seen has yielded the chemical 



