CHAPTER XXXIX* 

 NERVOUS SYSTEM— GENERAL METHODS 



977. Introduction. The methods for the microscopical investi- 

 gation of the nervous systems can be subdivided into two groups 

 which are spoken of as the cytological and anatomical methods 

 respectively. Those belonging to the first group are chiefly 

 meant for the study of the intimate structure of nerve-cells, 

 nerve-fibres and their supporting tissues ; those forming the second 

 group are more particularly suitable for investigating the mor- 

 phology of nerve-cells and their connections with one another and 

 with the nerve-fibres, as well as the architectural arrangement of 

 both nerve-cells and nerve-fibres in the various regions of the 

 central nervous system. This subdivision has mainly a descriptive 

 purpose, because methods which were originally proposed for the 

 study of the nerve-cell structure were afterwards found useful 

 for investigating the distribution of nerve-cells in the grey sub- 

 stance, while on the other hand slight modifications of anatomical 

 methods have led to the discovery of important cytological details. 



The methods for the study of the nerve-tissue in peripheral 

 organs having been described in the chapters on " Methylen 

 Blue," " Impregnation Methods," " Tegumentary Organs " and 

 " Muscle and Tendon," the following chapters are meant chiefly for 

 the description of methods for the investigation of the central 

 nervous system. 



FIXATION 



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

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

 in the case of 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 the capital advan- 

 tage of greatly helping to prevent distortion of the nerve-tissues 

 during their subsequent treatment. 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 man, but particularly 

 for a preliminary fixation and hardening of the very soft cerebral 

 mass of young individuals, which is particularly liable to injury 

 and. distortion in the process of removing it from the brain case. 



The choice of the fluid to be injected depends upon the object 

 * Revised by J. G. G. and R. O. S. 



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