APPENDIX A 259 



Osmic Acid is used in o'l-i'o per cent solution in water, for 

 fixing and hardening protoplasm : it also stains fats black. The 

 solution should be kept in a well-stoppered bottle in the dark. 



Paraffin is used as an embedding medium for small or delicate 

 objects. Paraffins of varying hardness and temperature of 

 melting-point may be obtained : the best for ordinary use is a 

 mixture which shall melt at a temperature of 50 to 60 C. 



Phenol (Carbolic Acid). Used, together with hydrochloric 

 acid, as a test for lignin. The best preparation of it is its solu- 

 tion in hydrochloric acid ; this is prepared by dissolving carbolic 

 acid in warm hydrochloric acid, adding, whilst the mixture is 

 cooling, sufficient hydrochloric acid to dissolve any precipitate 

 that may be formed. Lignified cells, treated with this mixture 

 and exposed to sunlight, assume a bright green colour in con- 

 sequence of the presence of coniferin. It may also be used, 

 instead of creosote, together with turpentine, as a clearing 

 agent, before mounting in Canada balsam. A small quantity 

 is to be added to glycerine jelly to prevent the growth of 

 Fungi. 



Phiorogriucin. Dissolve some phloroglucin in methylated 

 spirit, and gradually add strong hydrochloric acid till precipita- 

 tion begins ; the liquid is then ready for use : in sections treated 

 with it lignified walls assume a bright red colour. 



Picric Acid. A saturated solution in water is very generally 

 used for fixing the protoplasm of the cell as nearly as possible 

 in the form which it held during life. It is, however, objection- 

 able, owing to the difficulty in completely washing it out from 

 the specimens before hardening in alcohol, and in most cases 

 treatment at once with absolute alcohol is to be preferred. In 

 some cases, such as delicate Algae, it is well to dilute the 

 saturated solution with an equal volume of water. 



Picro-carmine (or ammoniun picro-carminate) is prepared 

 by adding a strong ammoniacal solution of carmine to a quantity 

 of concentrated solution of picric acid in water, until a precipi- 

 tate begins to be formed ; it is then evaporated to about one- 

 fifth of its bulk, filtered, and the filtrate is evaporated to dryness. 

 The crystalline residue is dissolved in water so as to make a 5 

 per cent, solution, and this may be diluted as occasion requires. 



S 2 



