Journal of Applied Microscopy. 29S 



with a screw chuck to carry laps, so arranged that the laps screw to a seat with 

 great perfection. Above and parallel to lathe spindle is a shaft in adjustable 

 bearings ; from this depends an arm or carrier, the face of which is arranged to 

 receive and clamp with great accuracy cast-iron grinding blocks, about 3 x 2 x i^ 

 inches in size. I use lead, copper, and " Scotch Water of Ayr" laps, which are 

 turned true on this lathe. These laps after turning are ground one against 

 another to perfect truth of surface. The grinding block, which when in the 

 carrier can swing and be withdrawn from the lap, but is held truly parallel to 

 the face of the lap, is now ground perfectly true to the lap. I use carborundum 

 in four grades, from grains to that which requires fifteen minutes to settle. I 

 grind with water from a chemist's wash bottle. Use the grains on the lead 

 lap, the powders on the copper, finish with stone lap and water. The process 

 can be divided into four heads: (1) preparation of material; ("2) imbedding; 

 (3) grinding; (4) mounting. 



1. Preparation of Material. — {a) Teeth work best that are started "green," 

 i. e., that have never been allowed to dry out, for drying develops many 

 small cracks, especially in the enamel. If the teeth need cleansing, wash 

 them in dilute lye. Preserve in turpentine. Make rough sections with a 

 ribbon or hack-saw. Make these sections thick, not less one -sixth the 

 length of the section, if possible. Where the saw cannot be used, grind away 

 half of the tooth and make the section of the remaining one-half. True the 

 surface roughly which is intended for the section. Wash carefully, picking out 

 any grains of carborundum, and removing any soft tissues that it is not specially 

 desirable to leave, as these are very apt to cause trouble. (/;) Bones: Secure, 

 if possible, fresh bone. Cut into short pieces, and macerate in water till all soft 

 tissues are removed. Bone from the dissecting hall, where subjects have been 

 injected, is not well suited for this purpose, though, when well cleaned and 

 selected, gives very good results. Saw the bone into rough sections as desired, 

 with the hack-saw, being careful that the thickness is never less than one-sixth 

 the greatest dimension. 



2. Imbedding. The material, after being washed and cleansed of all grit 

 and dust, is dehydrated in alcohol. For imbedding as well as for cementing the 

 sections to grinding blocks, prepare some hard balsam. Take a commercial 

 grade of balsam and dry it over a gentle heat till, when cold, it will receive the 

 impression of the finger nail under steady pressure, but flies to pieces under 

 shock. The material being dehydrated, pass it into chloroform ; after a day add 

 hard balsam from time to time for a week or ten days till the solution is syrupy, 

 then pour off the solution and dry the material for a week or more, so that when 

 cleaned of surplus balsam it shows no stickiness. 



3. Gri?iding. — {a) Teeth: Clean away from the material all surplus balsam. 

 Coat the surface of a grinding block with hard balsam. Arrange on this, section 

 surface down, as many sections as can be placed on the surface, warm on the 

 metal table, not to boiling, press each section carefully down into its place, cool, 

 put into carrier, grind with coarse powder till a supporting surface is developed, 

 supporting as nearly as possible the whole of each section surface. True this 

 supporting surface accurately. Take a second grinding block, heat on the metal 



