APPENDIX. 105 



any rupture of the same. A solution of alum is also often 

 used in the preservation of some of the Algae : a fluid still 

 better is the acetate of alumina, prepared by dissolving alum 

 in acetic acid, crystallizing by evaporation, and to a satu- 

 rated solution of this salt adding four or five parts of distilled 

 water ; or the acetate of alumina may be dissolved in the 

 glycerine. 



Bone, Teeth, tyc. Sections of these substances, if required 

 to be mounted dry, are best made by cutting a thin section 

 with the fine saw, and finishing by grinding down with a file 

 until they are made as transparent as possible ; they may then 

 be mounted in a dry cell. The sections are best ground by 

 fixing them to a slip of glass with strong balsam ; the better 

 methods of preparation are: to cut a thin section after mace- 

 ration in hydrochloric acid diluted with two parts water, then 

 to mount in a cell with a fluid composed of acetic acid 1 part, 

 water 2 parts ; or the broken bone, tooth, &c. may be placed 

 in a fluid of 1 part glycerine, 1 part water, for a few hours, 

 then add gradually a mixture of glycerine and acetic acid 

 equal parts ; after a short time thin sections may be cut with 

 a fine scalpel. Mount in a preservative fluid, acetic acid 1 part, 

 water 3 parts ; or it may be mounted in glycerine, or glycerine 

 and acetic acid equal parts. 



Crystals. The formation of crystals, from saline and other 

 solutions, under the microscope yields an extremely interesting 

 and useful study, for example, the beautiful appearance of 

 the crystals of chloride of ammonium caused by holding for a 

 few seconds a glass slide that has had one drop of hydrochloric 

 acid spread over the surface, over the fumes or vapour 

 of ammonia : upon the gradual evaporating of this thin 

 film of fluid, fine feathery crystals are formed ; they are 

 produced by the ammonia combining with the hydrochloric 

 acid. These crystals may often be developed from the human 

 breath, more especially in certain forms of disease. 



Some forms of crystals are best produced by placing a drop 

 of the solution under a thin glass cover and letting the fluid 

 evaporate gradually. The majority of crystals formed from the 

 various salts &c. are best mounted in castor -oil and sealed 



