MOUNTING MEDIA. 



Aluminium Acetate. 



In a saturated aqueous solution this salt forms a good mount- 

 ing medium for many delicate organisms. Most algae can be pre- 

 served in this way without any deterioration, while such objects as 

 the young prothallia of ferns can be kept without shrinking or 

 losing much of the brightness of their chlorophyll or protein 

 granules. Like all liquid mounting media it must be used in a 

 cell, and the slide should lie for 24 hours before sealing. 



Balsam. 



Balsam forms a most excellent and substantial mounting 

 medium. Sections mounted in it should be free from water and 

 this can be easily brought about by the use of alcohol. It is best 

 to begin with alcohol of moderate strength (50 per cent.), and 

 gradually increase it until the tissue is taken from that of 95 per 

 cent, strength. Before mounting, the sections must be cleared of 

 alcohol by the use of turpentine, chloroform, oil of cloves, or bet- 

 ter, a mixture of 3 parts of turpentine and 2 of pure carbolic acid. 



Balsam is prepared by evaporating over a gentle heat common 

 commercial Balsam of fir until the volatile oils have been driven 

 off and the residue becomes brittle. The portion that remains is 

 then dissolved in cedar oil, xylol, or chloroform, and filtered 

 through glass wool in a paper funnel. The medium should, at 

 the ordinary temperature, be of the consistency of a thick syrup. 

 Care must be taken to keep air bubbles from balsam. If, however, 

 they get under the cover they can be driven out if the slide be left 

 in a warm place for a few hours. 



