io8 Journal of Comparative Neurology. 



this is a suitable means of preservation for pieces destined for a 

 particular investigation of long duration. 



"One of the most interesting peculiarities of the process 

 which I here describe consists in the fact that, while the brown- 

 ish black stain acts quite similarly upon all elements of the 

 nervous tissue (various kinds of ganglion cells, nerve-fibers, 

 elements of the neuroglia and walls of vessels), yet in reality 

 the staining of all these at one time forms an exception, i.e. 

 when the elements are in a certain state of hardening which one 

 only happens upon accidentally in a great number of trials. As 

 a rule the reaction appears only partially, i.e. it affects only one 

 or another layer with gradations and combinations which one 

 may term endless. 



"This peculiarity does not detract from the method, but 

 is rather among its advantages, for if the reaction affected all 

 kinds of elements at the same time there would evidently arise 

 such an inextricable confusion that it would be impossible to 

 orient oneself in respect to the locations and relations of the in- 

 dividual parts. When, for example, in one preparation the 

 the cells especially are stained black, in another principally 

 the neuroglia together with the vessels and some groups of 

 nerve cells, it is evident that one can by the comparison of 

 many preparations obtain a general view of the various pecu- 

 liarities of the arrangement and relations to each other of the 

 individual species of elements and of the connection of the 

 structures of various regions. 



"This is so much the more the case since these combina- 

 tions and gradations also appear in certain layers and different 

 zones into which one is accustomed to divide different regions 

 of the nervous system. In the cortex, for example, the reaction 

 appears, with the various combinations above mentioned, some- 

 times in the superficial or middle, sometimes in the deep layers. 



" A law undoubtedly exists governing the manner of de- 

 velopment of the black stain and the succession of the reaction 

 among the various kinds of elements and it would be interest- 

 ing to learn to know this so as to be able to bring about one or 

 another result at will ; but it is extremely difficult, if not im- 



