68 APPENDIX TO PART I. 



time being constantly stirred, until the fluid has 

 become clear, after which it is filtered through 

 glass wool. 



This glycerine jelly, which, in a thin layer, is 

 completely transparent and as clear as water, is 

 useful for preparations that are to lie immovably 

 under the cover-glass, but which are too small to 

 be held by the pressure of the latter. Pollen 

 grains, starch, yeast-cells, spores, and especially 

 unicellular algae, e. g. Desmidiacae, should be 

 mounted in this medium. If it is desired to pre- 

 serve the structure of the protoplasm and the 

 arrangement of the chlorophyll bodies as far as 

 possible, the plants must be previously hardened 

 by immersion in an aqueous solution of perosmic 

 acid (i : 800) or in absolute alcohol. After being 

 hardened the preparations are placed in dilute 

 glycerine before being mounted in glycerine jelly. 

 When this is cold the cover-glass is sealed. 



[Taking advantage of the insolubility of gela- 

 tine which has been acted upon by potassium 

 bichromate and exposed to the light, Dr. Goodale 

 has recommended lightly painting the edge of the 

 cover-glass with a solution of this salt in place of 

 the usual ring of varnish. W. T.] 



CHLORIDE OF CALCIUM is often used in aqueous 

 solution for many kinds of preparations, starch, 

 however, excepted. One part of chloride of cal- 

 cium to three of distilled water, with a trace of 

 hydrochloric acid (to prevent crystallization under 



