578 



NEKVOUS SYSTEM. 



ingly difficult. Sections of the nerve-centres must be prepared with great care, and 

 they are not easily made and preserved. In the numerous anatomical investigations that 

 have been made within the last few years, the centres have generally been hardened 

 artificially; and almost every investigator has used different processes and reagents, 

 which may account in a measure for the differences of opinion that now exist upon all 

 points connected with the minute anatomy of these parts. 



There is, at the present time, considerable discussion with regard to the intimate 

 structure of 'the substance of the nerve-cells, their nuclei and nucleoli, and the points 

 involved have a certain amount of physiological interest. In the first place, the transverse 

 striae in the axis-cylinder treated with nitrate of silver, noted by Frommann and confirmed 

 by Grandry and others, have been observed by Grandry in the substance of the nerve- 

 cells. While this fact, perhaps, shows that the substance contained in the cells and their 

 prolongations is the same as the substance of the axis-cylinder, as we stated with regard 

 to the axis-cylinder, it is possible that the markings may be entirely artificial, and that 

 they do not demonstrate the existence of two distinct substances in the tissue. 



FIG. 183. Trawvertsc section of the gray substance of the anterior cornua of the spinal ccrd of the oa\ treated 



with nitrate of silver. (Grandry.) 



The most interesting question with regard to the structure of the nerve-cells relates 

 to the mode of origin of their fibres or poles. Until quite recently, these have been 

 regarded as simple prolongations of the substance of the cells ; but lately the view has 

 been advanced that the nerve-cells, in the human subject, are composed of regular fibrils 

 continuous with the poles and starting, as it were, from the nucleoli. The fibrillation of 

 the nerve-cells and their prolongations is figured by Schultze in an article in one of the 

 most authoritative of the recent works on histology (Strieker) ; but some other eminent 

 observers have failed to note the appearances here described, at least in the human sub- 

 ject and in the mammalia. With our present knowledge of the physiology of the nerve- 

 cells, the question whether or not their substance be fibrillated has little more than .an 

 anatomical interest ; but there can be no doubt that the cells in some of the lower orders 



