110 VEGETABLE HISTOLOGY. 



ever medium it is to be mounted, must be saturated with a fluid 

 not very different from the mounting medium. For example, 

 to mount in gelatin, the object must be transferred from gly- 

 cerin; in balsam, from cloves, turpentine, etc.; in Farrant's 

 medium, from glycerin. Media which do not harden or which 

 absorb moisture, as glycerin-gelatin, must be closed in with a 

 ring of cement. (See mounting media, page 104.) 



SCHEME FOR MAKING PERMANENT MOUNTS. 



The specimens are supposed to be alcoholic ; if not, they are 

 to be placed for a time in dilute alcohol. Alcoholic objects take 

 the stains better than fresh tissues. In the following scheme 

 the sections are supposed to be free from any imbedding mate- 

 rial. The procedure for mounting paraffin or celloidin sections 

 has already been stated under Section Cutting. 



BALSAM MOUNTS. If the section be lying in alcohol 



1. Wash in water if it is to be stained in aqueous stains. 



2. Transfer to staining liquid. Choose stains according to 

 the nature of the cells that it is desired to stain. Aniline stains 

 color chiefly woody or lignified material. If the stains are in 

 alcoholic solutions take objects from alcohol of about same 

 strength. The time required will vary according to the nature 

 and strength of the stains and is best learned by actual practice 

 with them. The sections should be examined at intervals for 

 depth of color by transferring them to water or alcohol and then 

 back again to the staining liquid. After one has stained a few 

 sections he obtains an idea of the exact time required to attain 

 proper color effects. 



3. Wash off the superfluous stain .by moving the section 

 about in water. 



4. Dehydrate the section by passing it into 70 per cent, 

 alcohol 3 minutes, 90 per cent, alcohol 5 minutes, absolute alco- 

 hol (distilled from lime) 5 or more minutes. 



5. Place the section next in a clearing agent, as oil of cloves 

 or turpentine, 5 minutes or more. If section be not completely 

 dehydrated it will now appear opaque. It must then be passed 

 back to the absolute alcohol and back again to the clearing 

 reagent. 



6. Transfer the section from the clearing agent to a slide 

 and remove the excess of the former. Place upon it a drop of 

 balsam and then a cover glass, avoiding air-bubbles. 



GLYCERIN-GELATIN MOUNTS. Steps 1, 2, 3 are the same as 

 above. 



4. Pass the section into weak glycerin 3 to 5 minutes. 



5. Then into stronger glycerin 3 to 5 minutes. 



6. From 5 into concentrated glycerin 5 minutes. 



