20 INTRODUCTION. 



alcoholic solution of anilin green. In a, row of watch-cr3-stals 

 the following hquids are placed: (1) water, (2) Woodward's 

 carmiu, (3, 4, 5) alcohol, (G) absolute alcohol, (7) oil of cloves. 

 Tlie specimen, taken from the green, is dipped for a moment in 

 water, tlien for about a minute in the carmin, then successively 

 through the alcohols, in each of wiiich it remains ten to twenty 

 minutes, except in the first, where it remains only long enough 

 to have the unfixed carmin washed awa3\ From the last alcohol 

 it goes into oil of cloves (or benzol), where it should remain 

 long enough to become perfectly transparent. It is then to be 

 mounted in balsam. 



96. Double-staining can also be effected bj- the successive use 

 of haematox3'lin and an anihn color. Bj- the use of two or more 

 anilin dyes different parts of a specimen may be colored differ- 

 ently ; but as a rule all these effects are uncertain, and cannot be 

 relied upon for the positive identification of tissues. In general, 

 however, long bast fibi-es take characteristic colors. 



97. Tlie following combinations for double-staining are rec- 

 ommended bj- Dr. Stirling,' and though originallj- designed only 

 for animal tissues, serve well with sections of plants : — 



1. Osmic acid and picrocarmin. 2. Picric acid and picro- 

 carmin. 3. Picrocarmin and logwood (hsematoxylin). 4. Pi- 

 crocarmin and an anilin dj-e. 5. Logwood and iodine green. 

 6. Elosin and iodine green. 7. Eosin and logwood. 8. Gold 

 chloride and an anilin dye. 



98. In the cases which require special treatment, for instance, 

 the staining of the nucleus, the precautions laid down must 

 be attended to in order to insure success. But in the ordinary 

 instances where it is desirable to stain a specimen merely to 

 bring some part into prominence for purposes of demonstration, 

 the widest choice in d3-es and their use is advised. A few mor- 

 dants liave been tried in order to fix the colors, but with little 

 success. The best are tannin in solution, and aqueous solutions 

 of an3' of the alums. A little practice will show which mordant 

 is best for each case. 



99. Specimens stained 1)3' nearly all of the above d\'es can 

 be mounted securely in balsam, as directed in section 110 ; but 

 glycerin and glycerin-jelly mounts are apt to become faded or 

 discolored after a time. 



100. Mounting-media. Pollen and other dr3' specimens are 

 preserved in shallow cells formed by a thin ring of asphalt- 



1 Journ. Anat. and Phys., 1881, p, 349. 



