294 Journal of Applied Microscopy. 



table, coat with balsam, remove to a wooden support, press into this softened 

 balsam quickly and accurately, using only as much pressure as can be given with 

 the hand, the supporting surface of sections. Before the sections can become 

 heated through, plunge the whole in cold water ; when thoroughly cold, wipe off 

 and place on hot table with first block down. As soon as the water between the 

 blocks begins to boil, slip block No. 1 quickly off and plunge block No. '2 with 

 sections into cold water. Place the block into the carrier, grind with medium 

 powder till the sections all show a surface suitable for finished sections. Polish 

 the surface with finest powder, then with the stone lap, and finally with dry 

 whiting powder and the hand. After polishing carefully, wash with water, being 

 careful to remove all powder or grit of any kind, dry the surface carefully, and 

 wipe the surface with the finger dipped into gasolene, using only the least 

 possible quantity of gasolene. Clean block No. I, heat it, and coat with balsam. 

 Transfer the sections to block No. 1, as outlined above, being very careful to 

 exert a uniform pressure in bringing the sections down on block No. 1. Grind 

 first with the grains of carborundum, then, as the sections get thin, use finer and 

 finer powder. If too coarse a grade of powder be used as the sections get thin, 

 the enamel will be broken and the sections will leave the block. When all color 

 in the enamel begins to disappear, use the stone lap, then grind till all color is 

 gone from the enamel, the dentine looks transparent, not white, and the block 

 seems to have only a coat of varnish on the surface. Polish with the palm of 

 the hand and whiting, wash in water, dry, wash in gasolene, dry, immerse in 

 benzole till the sections come away. {/>) Bone is prepared in the same way, 

 save that each section is roughly trued on one side before cementing to the 

 block; they are then cemented with trued surface down, and the section 

 surface is prepared directly, making only one transfer necessary in preparing 

 the sections. 



4. Mounting. — Tooth and bone sections may be mounted either dry or in 

 balsam. If the cells do not suffer with a deposit of " dew," the dry mounts are 

 the more permanent. The balsam mounts, if carefully made, will last in good 

 condition for many years, and I think are much finer. I prepare cells for dry 

 mounts with gelatine, and seal them with a fine ring of a hot thick solution of 

 gelatine, finishing in black or colors, as desired. It is essential that the sections 

 shall perfectly dry. the cell dry, and both quite warm when the cell is closed. 

 When made in this way I have lost few slides from " dewing." For balsam 

 mounts I use paper-filtered balsam. Dry this on a slide, in large excess, till 

 when cold it is nearly hartl, but not fiinty. \\'hile hot, coat with this one side of 

 a suitable cover-glass, allow both to cool. Place the section between the two and 

 press the cover down, using as little heat as possible. With a little practice and 

 dexterity all the air bubbles that show up about the section will be washed away. 

 Too much heat fills the section and ruins the mount. Cut away the excess of 

 balsam, and wash, first with gasolene, then with soap and water. 



As I have said, success depends upon attention to details. One grain of grit 

 out of place at a critical moment will spoil all the sections. I have ground over 

 one hundred sections of small teeth on one block at one time. I usually grind 

 twenty-five longitudinal sections of human teeth ;U once and I have made 



