42 Journal of Comparative Neurology. 



which is no real nerve-cell protoplasm, but a modified cell pro- 

 toplasm which is found partly within the nerve cell in the form 

 of fibrils, partly outside forming the enormous masses of (inter- 

 cellular) gray matter which is, anatomically, to be considered a 

 very delicate continuous net- work ('Gitterwerk') of elementary 

 fibrils, together with the much coarser pericellular net which 

 probably also consists of fibrillary substance and belongs al- 

 ready to the central gray matter, not to the cell-body; secondly, 

 it appears in the form of fibrils as the most essential constituent 

 of the nerve fibers." Nissl gives two remarkably striking pic- 

 tures of pericellular nets from Bethe specimens, and three illus- 

 trations of cortex of the mole, of the dog, and of man, from 

 corresponding regions, showing very clearly the greater amount 

 of * gray matter ' between the cells in man. (The higher the 

 development of an animal, the fewer the nerve-cells in an equally 

 large space of cortex.) The comparison shows that the superficial 

 layer of the cortex varies least ; an increase in ' gray matter ' 

 is largely visible in the second and third layer. Nissl says (page 

 1028) correctly that any hypothesis must be dropped (we should 

 say modified) as soon as even one single fact has been demon- 

 strated to disagree with it. With this insight he proceeds to 

 undo the neurone-theory ' once forever, ' and even his own hy- 

 pothesis of specific nerve-cell function, since he has ' discov- 

 ered ' the * gray substance ' and the fact that the cell changes 

 described by him cannot be an expression of disturbed function 

 but merely that of a chemical or physical alteration. The ex- 

 istence of various cell-types in the nervous system is none the 

 less evident to him. The more elaborate forms of function in 

 the highest species of the animal series undoubtedly depend on 

 an increasing division of labor of the cells in the higher cell- 

 communities. ' From this point of view the idea, somewhat 

 strange to our usual thought, becomes intelligible (?), that the 

 highest functions of the vertebrate body are not directly at- 

 tached to cells, but to a living substance, the morphological 

 arrangement of which reminds one much rather of anything 

 else than of cells. We need only look into our body carefully 



