SECTIONS OF CEREBRAL AND CEREBELLAR CORTEX. 71 



with a very weak acid solution, the best wash being a half 

 to one per cent, solution of glacial acetic acid. Small por- 

 tions of the cortex, a third of an inch in thickness, are pre- 

 viously hardened in the bichromate of potash or in Muller's 

 fluid, using chromic acid solutions as accessories to hurry on 

 the process near its completion, are then transferred to 

 Stirling's microtome and the finest possible sections made. 

 They should now be placed for a few minutes in methylated 

 spirit, and next passed into Beale's carmine solution, diluted 

 Avith seven times its bulk of distilled water. I find my 

 sections are usually stained to the requisite depth of colour in 

 six or eight hours, but variations in rapidity will constantly 

 occur, the delay being frequently occasioned by the presence 

 of free chromic acid, which should always be completely 

 removed by immersion in spirit prior to section cutting; 

 and we can readily conceive with Beale that any changes 

 undergone by commencing putrefaction in the nuclei will, 

 by altering the acid reaction Avhich is the natural post- 

 mortem condition, interfere with the necessary decomposition 

 of the carminate. Sections that have assumed the proper 

 tint may now be removed to a capsule containing a half per 

 cent, solution of glacial acetic acid. They are next washed 

 from all acid, dehydrated by steeping in absolute alcohol or 

 rectified spirit, cleared with oil of cloves or anise, and 

 mounted in balsam. This is the usual method adopted by 

 me in single staining with carmine, bat the results, though 

 good, are by no means so uniformly satisfactory as by log- 

 wood and aniline processes. There is one measure, however, 

 which 1 adopt with this reagent with the best results ; I may 

 denominate my process as a mode of differentiation by peculiar 

 alterations in the refractive indices of the structural elements. 

 Changes which occur to the cell-contents and their processes 

 — I refer to alterations in density by the agency of heat, 

 spirit, coagulating media, and the essential oils — alter the 

 refractive relationships previously held by them to the sur- 

 rounding matrix, and thus bring into view what would 

 otherwise be passed by unnoticed. It appears to me that 

 this variety of histological analysis may, in regard to brain 

 sections, be turned to very good account. On placing an 

 unstained section of cerebrum or cerebellum in the field of 

 the microscope, saturated with spirit, little or no structure is 

 apparent, but if a drop of essential oil be now allowed to run 

 over it there will be observed at a certain stage of the clear- 

 ing up, and whilst the spirit is evaporating, a sudden start- 

 ing out in bold relief of the cells, nerve-fibres, vessels, «&c., 

 which again disappear or partially fade on perfect clearing 



