CHAPTER XXXI.* 



NERVOUS SYSTEM GENERAL METHODS. 



805. Introduction. The microscopic investigation of the nervous 

 system pursues two ends. Either it is desired to elucidate the 

 intimate structure of nerve-cells, nerve-fibres and their supporting 

 tissues, or to study the morphology of nerve-cells, their distribution 

 in the grey matter, their connections with each other, and with the 

 nerve fibres which chiefly constitute the white matter, and lastly to 

 investigate the architectural arrangement of both nerve-cells and 

 nerve-fibres in the various regions of the central nervous system. 

 The processes employed in the first case form a group of cytological 

 methods, whilst the processes used in the second instance are spoken 

 of as the anatomical methods. 



The processes used in the study of nervous tissue in peripheral 

 organs having been described in the chapter on " Methylene Blue," 

 " Impregnation Methods," " Tegumentary Organs," and " Muscle 

 and Tendon," the following chapters are chiefly devoted to the 

 description of methods for the investigation of the central nervous 

 system. 



Fixation. 



806. Fixation by Injection. Fixation, in the proper sense of the 

 word, is of course out of the question for the human subject. But 

 in the case of the lower animals it is possible to inject fixing fluids 

 into their nervous centres when still in an almost living state. The 

 practice ensures a very rapid penetration into and even distribution 

 within the tissues of the fixing agents, and has, moreover, the capital 

 advantage of greatly helping to prevent distortion of the nerve- 

 tissues during their subsequent treatment. And as in most instances 

 the practice does not meet with special difficulties, it should be 

 adopted as far as possible also in the case of human subjects, but 

 particularly for a preliminary fixation and hardening of the very 

 soft cerebral mass of young individuals, which is particularly liable 

 to much injury and distortion in the process of removing it from 

 the brain case. 



* Kevised and in great part rewritten by Dr. C. Da Fano, King's 

 College, University of London. 



