138 MICROSCOPIC OBJECTS. 



and water freely until the surface has received a good 

 polish. 



In grinding, smoothing, and polishing, the directions 

 in which the fossils are to be rubbed must be varied 

 continually, so that the tool be worn uniformly and not 

 become either hoUow or convex. 



The process of grinding, smoothing and polishing will 

 be greatly facilitated, and the labour reduced consider- 

 ably, if the tools are made to revolve during the 

 working. 



On Preparing thin sections of Teeth, Bone, and similar 

 Substances. — ^These materials should be cut into very thin 

 slices with fine saws made for the purpose of pieces of 

 watch-spring, &c. They are then to be ground upon a 

 hone, or water-of-ayre stone, with water, when they wiU 

 be ready for mounting. 



To Prepare thin sections of Coal. — These are cut with 

 a saw, and afterwards ground on a fine sand- stone with 

 water. 



To Prepare Skins of the Larvce of Insects. — Some 

 require to be immersed quickly in boiling water, then 

 taken out and plunged into strong acetic acid for a few 

 minutes ; others only require to be soaked in cold water ; 

 and some kinds require no such preparatory process. 

 Make an incision along the back, beginning at the tail 

 and passmg the point of the scissors along towards the 

 head. When laid open the inside must be washed out ; 

 and if the subject is a terrestrial larva, the trachea must 

 be separated at each of the several spiraculse, along each 



