-,r THE 



DIVERSITY 



OF 



THE HISTOLOGICAL TECHNIQUE 



BY OLIVER S. STRONG, M.A., PH.D. 



TUTOR IN BIOLOGY, COLUMBIA COLLEGE 



THE Golgi methods of staining nerve cells and their processes are known as impregnation 

 methods in which metallic salts are precipitated in or around the elements, thus bringing them 

 into clear relief. The nerve cell and its processes appear as a black silhouette upon a yel- 

 lowish or whitish ground. Golgi has employed both silver and corrosive sublimate methods. 

 It is the former only which have been used in the preparation of the specimens shown in 

 this atlas. 



In the silver methods the tissue is first hardened in a solution of potassium bichromate 

 and then brought into a solution of silver nitrate. If the tissue is in the proper stage of 

 hardening, the silver is deposited (probably principally in the form of silver chromate) in and 

 around certain of the nervous elements. As the remainder of the tissue remains unstained 

 the sharp contrast thus afforded enables one to trace the finest ramifications of the nervous 

 elements impregnated. 



It is a peculiarity of these methods that all the elements present in the tissue are very 

 rarely impregnated at one time, and those elements which are thus picked out by the stain 

 are more or less different in each preparation. Owing to this peculiarity, the various nerve 

 cells with all their processes can be distinguished separately. Were all the cells and processes 

 present stained at once, there would be simply an inextricable mass of black-stained cells and 

 fibres. 



The silver methods may be subdivided as follows : 



(a] Golgis long method, in which potassium bichromate alone is used in hardening the 

 tissue before placing it in the silver nitrate. This process requires nearly a month to harden 

 the tissue properly. 



(b] Golgi 's rapid method, in which a mixture of potassium bichromate and osmic acid is 

 used to harden. Here the time required is reduced to a week or less. 



(c] Golgi's mixed method, in which the tissue is placed first in potassium bichromate for 

 from a few days to a month and then in the osmic-bichromate mixture. 



