REVIEW OF THE GOLGI METHOD. 83 



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 individual parts. 

 When, for example, in one preparation 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 peculiarities 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 combinations 

 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, sometimes in the 

 superficial or middle, sometimes in the deep layers. 



"A law undoubtedly exists governing the manner of develop- 

 ment of the black stain and the succession of the reaction among 

 the various kinds of elements, and it would be interesting 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 impossible, to attain 

 this. This difficulty will be readily comprehended when one 

 reflects that the diversity of results is brought about not only by 

 the conditions given already, but also by the unequal hardening 

 action of the bichromate, so that the individual layers of the 

 pieces are in different conditions. In the individual pieces the 

 degree of hardening may increase from centre to periphery, so 

 that a number of the above combinations and gradations may 

 appear in one piece. 



"The following approximate rule, however, may be accepted 

 for the way the reaction enters the various elements of the nervous 

 tissue when a number of similar pieces are successively subjected 

 to the action of the silver nitrate. Then stain in the following 

 order : — 



" I. — The bundles of nerve fibres. At the same time with the 

 staining of these fibres some scattered ganglion cells which lie 

 dispersed in the gray matter appear. 



" The staining of the nerve-fibres at the beginning shows little 



