APPENDIX. 



761. Green Light. The employment of green light iii microscopy has 

 been alluded to above ( 606) as recommended by Rabl. The suggestion is, 

 I believe, due to ENGELMANN (Pfliiger's Arch., 1880, p. 550). He strongly 

 recommends the use of green light for delicate observations as giving 

 sharper definition, allowing finer detail to be seen, and tiring the eyes less 

 than white light. Green glass of sufficiently good quality is found in 

 commerce. The glass is best put between the mirror and the object, e. g. on 

 the diaphragm. Blue glass (cobalt or ammonio-sulphate of copper) is also 

 useful, but less so than green. Red light is most hurtful. " The explana- 

 tion of these points, so important in practice, may be found in the results 

 obtained by Lamansky in his researches on the " Limits of sensibility of the 

 eye to the different colours of the spectrum" (Arch. f. Ophthalm., xvii, 

 p. 123, 1871)." 



762. Cleaning Slides and Covers (HANAMAN, Journ. Roy. Mic. Soc., 

 i, 1878, p. 295 ; American Naturalist, xii, p. 573). To a cold saturated 

 solution of bichromate of potash, add of its bulk of strong sulphuric acid 

 (care must be taken on account of the heat and vapours evolved). 



(HENEAGE GIBBES, ibid., iii, 1880, p. 392). Place the cover-glasses in 

 strong sulphuric acid for an hour or two, wash well until the drainings give 

 no acid reaction ; wash first with methylated spirit, and then with absolute 

 alcohol, and wipe carefully with an old silk handkerchief. 



(SEILER, ibid., p. 508). New slides and covers are placed for a few 

 hours in the following solution : 



Bichromate of potash 2 ounces. 



Sulphuric acid ....... 3 fluid ounces. 



Water 25 



Wash with water. The slides may be simply drained dry ; the covers 

 may be wiped dry with a linen rag. 



Slides and covers that have been used for mounting either with balsam or 

 a watery medium are treated as follows : The covers are pushed into a 

 mixture of equal parts of alcohol and hydrochloric acid, and after a few days 

 are put into the bichromate solution and treated like new ones. The slides 

 are scraped free of the mounting medium with a knife and put directly into 

 the bichromate solution. 



FOL (Lehrb., p. 132) recommends either a solution containing 3 parts of 

 bichromate, 3 of sulphuric acid, and 40 of water ; or simply dilute nitric 

 acid. 



