144 H OW TO WORK 



chemical solutions adapted to render the anatomical elements of these 

 tissues distinct. There can be no doubt that modes of investigation 

 will at length be found out which will enable us to demonstrate satis- 

 factorily the relation of the delicate structures which make up the 

 nervous system, to each other. The student should try for himself 

 a number of fluids of different composition. I cannot too strongly 

 recommend the plan invented by Mr. Lockhart Clarke, which is 

 given below, for carrying out enquiries of this nature. 



If a portion of white cerebral matter be treated with water, the 

 nerve fibres soon become changed in character, apparently in conse- 

 quence of the partial separation of the oily from the albuminous 

 constituents which are contained within the tubular sheath. The oily 

 matter forms distinct and separate globules, often of considerable 

 size, or it tends to collect in quantity in different parts of the fibre, 

 which produces a beaded appearance. A similar change takes place 

 in nerve fibres generally, if they are not examined very recently, or 

 if they have been soaked for a short time in water. In fig. 196, 

 pi. XXX, some of these changes are represented. 



244. Examination of the Spinal Cord. Different parts of the 

 cord may be examined in the fresh state, but in order to demonstrate 

 the beautiful structure described and figured in modern works, we 

 must have recourse to certain methods of preparation. A weak solu- 

 tion of chromic acid is invaluable for investigating the structure of the 

 cord. Segments of different parts are placed in the solution and 

 allowed to harden, when very thin sections may be readily obtained 

 and examined. 



The method of preparation followed by Mr. J. Lockhart Clarke, 

 in his beautiful and highly important investigations on the structure 

 of the spinal cord was the following : 



A perfectly fresh cord was hardened in spirits of wine, so that 

 extremely thin sections, in various directions, could be made by 

 means of a very sharp knife. A section so made was placed on a 

 glass slide, and treated with a mixture composed of one part of 

 acetic acid and three of spirits of wine, which not only makes the 

 nerves and fibrous portion more distinct and conspicuous, but renders 

 also the grey substance much more transparent. The section was 

 then covered with thin glass, and viewed first by reflected light with 

 low magnifying powers, and then by transmitted light with higher 

 ones. 



According to the second method, the section is first macerated 

 for an hour or two in the mixture of acetic acid and spirit. It is then 

 removed into pure spirit, and allowed to remain there for about the 

 same space of time. From the spirit it is transferred to oil of turpentine, 



