142 Modern Microscopy 



may remain there until required. The embedded mass can 

 now be placed between two pieces of carrot, and put into an 

 ordinary microtome, and the sections made with a knife or 

 razor, which must be well wetted with methylated spirit ; 

 or the embedded specimen can be removed from the 

 cork, and, after soaking in water, it can be transferred to 

 gum and syrup, and the sections made with a Cathcart 

 freezing microtome. If it is desired to remove the celloidin 

 from the sections, soak them in equal parts of absolute 

 alcohol and ether. When all the celloidin is removed, 

 transfer to distilled water, then into the stain. After stain- 

 ing, wash in distilled water, dehydrate, clear in clove oil, 

 and mount in Canada balsam. 



When it is not desirable to remove the celloidin from the 

 sections, they should be stained in borax carmine or hsema- 

 toxylin. The former stains celloidin, but the colour is 

 removed by washing in acidulated alcohol. Hematoxylin 

 only stains it slightly. All the aniline dyes stain it deeply ; 

 they should not be used. 



Tissues are usually stained in bulk before they are 

 infiltrated with celloidin. When so, the sections must be 

 dehydrated in methylated spirit, cleared in oil of bergamot 

 or origanum, and mounted in Canada balsam. 



When desirable, sections infiltrated with celloidin may 

 be mounted in Farrant's medium or glycerine Jelly. Wash 

 away all trace of alcohol with water, and mount in either of 

 the above media in the ordinary way. 



Celloidin is an excellent medium for infiltrating many 

 specimens of both animal and vegetable subjects. The 

 following are a few of these : 



Flower-buds of lily, yucca, evening primrose, poppy, 

 dandelion, and anthers ; worms, leech, flukes, gills 

 and organs of mussels, heads of frogs, newts, sponges, 

 etc. 



For flower-buds proceed as follows : Harden the bud in 

 methylated spirit in the ordinary way. Then take a piece 

 of fine silk or cotton and tie it round the centre of the bud to 



