THE MICROSCOPE AND HOW TO USE IT. 103 



(sometimes 24 hours will suffice), to ensure them against 

 subsequent decomposition. If the brain is the subject of research, 

 leave it for from four to six weeks to harden in the following 

 solution : — Chromic acid, i part ; bichromate of potash, 2 parts ; 

 water, 1,200 parts. If the spinal cord, then i part of the acid to 

 200 of water in the case of the human or large animal subject, or 

 I to 400 proportion in that of a small animal, will be sufficient to 

 induce the requisite induration. [Do not exceed the above-named 

 period of immersion, as the action may change and ruin the 

 specimen. Should you wish to defer your investigation, keep the 

 specimens in methylated spirit until ready to proceed with them.] 



II. Cutting. — A mixture of i part of lard to 5 of paraffin, 

 having been heated in a water bath, is poured into a microtome 

 or a tin or paper box (see Jour fial of Microscopy, Vol. VI., p. 242). 

 Now, having first steeped your specimen some ten minutes in 

 absolute alcohol, hold in forceps and dip gently into the 

 embedding mixture for a moment, withdraw to prevent shrinkage, 

 and then replace and hold it until the mass begins to cool. Then, 

 with a razor, kept wet in methylated spirit, (or absolute alcohol if 

 you desire very fine sections) ; cut sections, sweeping obliquely 

 from right to left across the top of the microtome, taking care to 

 remove each slice in one sweep. Transfer sections seriatim to 

 water (or spirit), removing the adhering paraffin, if any, by 

 moving them circularly with a small-hair brush ; then pour off the 

 water or spirit. Having washed them, leave for some thirty 

 minutes in a solution of i part bichromate of potash to 100 of 

 water ; then proceed to stain and mount in the ordinary way. 



Variation from above rules : — 



Freezing has been successfully used in preparing brain, etc. ; 

 after staining in carmine mount in a mixture of hydrochloric 

 acid, 2 minims, or glacial acetic acid, 5 minims, added to 

 glycerine, i oz. 



Sections of spinal cord should be taken from all the various 

 regions, and hardened in a solution of ammonia bichromate (2 or 

 5 per cent.) solution for from a week to a month, according to 

 what strength of solution was used ; transfer to spirit and cut. 

 Stain sections in eosin, carmine, hcematoxylin, lithium-carmine. 

 Anilin blue black, 1 7 per cent, solution stains the ganglion cells 



