184 H. R. OCTAVIUS SANKEY. 



receive a pencil-mark without danger of its being oblite- 

 rated. 



III. The next step in the process is to dry the stained 

 slices upon the glasses. They should be placed in an airy 

 and dry situation, but not, as a rule, subjected to heat, but 

 to a current of air. In certain states of the atmosphere, 

 however, they may require the assistance of a very moderate 

 degree of artificial heat. Or should the sections be very 

 thick, a slight amount of dry heat is required so as to antici- 

 pate any liability to putrefaction before desiccation has had 

 time to occur. When the sections are dry it will be found 

 that they are firmly adherent to the glass, and that they, as 

 a rule, show no tendency to crack, except just at the edges. 

 Should it be desirable to obtain a good view of the edge of 

 any section, a slice of unstained brain may be placed over 

 the stained piece so as to overlap the edge, which virtually 

 removes the edge it is desired to see from its external posi- 

 tion, and renders it far less liable to crack. 



IV. When the sections are properly dried they will be 

 found to be of the consistence of somewhat dry cheese, and 

 rather uneven in thickness. The next step is to bring them 

 to a condition suitable for microscopical examination, by re- 

 ducing them to the necessary thickness. The sections, before 

 they are reduced, may be described as consisting of three 

 layers — an upper, middle, and lower, the latter being in con- 

 tact \Aith the glass. It is obvious that the upper and the 

 lower, which were the parts in immediate contact with the 

 dye, will be more deeply stained than the central layer, which 

 in fact remains white. In reducing the thickness of the sec- 

 tions by paring, it is clear that if the upper layer is removed 

 but one of the deeply stained layers will remain. The object 

 to be gained by the paring is to reduce the section to the 

 lower stained layer only. The unstained or intermediate 

 layer may be removed as completely as practicable without 

 endangering the deeper blue layer ; but if any unstained 

 substance be left it is of not much consequence, as the pro- 

 cess of clearing renders it invisible. The operation of paring 

 can readily be performed with a razor, but it can be much 

 more efficiently and quickly accomplished by means of an 

 instrument that I have devised for the purpose. This in- 

 strument is a kind of plane, and is a modification of an 

 ordinary carpenter's two-inch skew rabbet-plane, but with 

 which I operate in the reverse position, that is, with the 

 cu tting edge uppermost. The modification consists in screw- 

 in g to the sides of the plane two slips of iron, having per- 

 ectly tr ue and level edges, which are also adjustable by set 



