16 MANUAL OF HISTOLOGY. 



melted. This having been done, a mould should be at hand to 

 receive both the embedding mixture and the piece of tissue. 

 Various moulds are in use. Some are made of tin-foil, and are 

 shaped like a common earthenware garden-pot. 



A fine, long cambric needle should be passed through the tis- 

 sue, and then (the mould being placed in position) the point of the 

 needle is to be pushed through the bottom into the table beneath. 



Then the mixture of the liquid wax and oil, which has been 

 heated to the point of melting and no more, should be poured 

 slowly into the mould, so as to slightly cover the specimen. 

 During the process of hardening, minute bubbles of air will be 

 liberated from the tissue ; they will escape more rapidly, and 

 the embedding material will harden more quickly arid thor- 

 oughly, if the microscopist blows gently and continuously on 

 the surface of the liquid. Just at the moment when the mass 

 is no longer liquid, the needle should be suddenly withdrawn. 



As soon as it is hard throughout, the tin-foil mould may be 

 torn off by breaking the edge at any point with the finger. 

 The foil tears like paper. 



When moulds are not at hand, an excellent substitute may 

 be made with ordinary writing paper. Some confectioners 

 make them of pressed paper. 



Embedding in glycerine and tragacantli. Mr. John Ste- 

 venson's plan is as follows : He takes two drachms of glyce- 

 rine and mixes them with one drachm and a half of powdered 

 gum tragacanth. The tissue to be cut is then placed in a small 

 pill-box, and the mixture poured in. The box is then laid 

 away in a cool place from eight to twelve hours, when sections 

 may be made with the knife. In case the specimen is to be 

 preserved for a longer time, the bottom of the box may be 

 taken off, and the side slit up. The specimen will now be 

 found embedded in a solid elastic cake, and may be slipped 

 into alcohol until required. When it is to be kept in spirits 

 less than twenty-eight hours, the mixture should be glycerine, 

 2 drachms ; powdered tragacanth, 1 drachm ; gum arabic, 15 

 grains. Tissues that have lain in spirit should be steeped in 

 cold water a few hours before embedding. 



The hand section-cutter is used by some microscopists. It 

 is simply a cylinder which is designed to receive the object 

 and the material in which it is embedded. A plunger, which 

 is driven up from beneath by the revolution of a screw, pushes 



