33 MOUNTING MEDIA. 



shrinking, sections to be mounted in glycerin should first be placed 

 in a mixture of equal parts of glycerin and water and allowed to 

 remain a little time, when stronger glycerin is added at intervals, 

 until the section is thoroughly permeated with the pure agent. As 

 this is hygroscopic, the mounts must be sealed at once as they will 

 readily absorb a quantity of water sufficient to dilute its strength 

 appreciably. The cover can be sealed first with a little glycerin 

 jelly, and, after this has hardened, with shellac or asphalt. 



Glycerin is a very good mounting medium for studying fresh 

 tissues, as it evaporates very slowly. Sections mounted in it can 

 be kept for examination for some time. Glycerin, like gtycerin 

 jelly, has the property of making sections clear or transparent. 

 They should therefore be treated with a permanent stain. Only 

 the purest commercial glycerin should be used, and this must be 

 kept in a tightly corked bottle, otherwise, it will absorb a sufficient 

 quantity of water to render it almost useless as a mounting 

 medium. 



Glycerin and Acetic Acid. 



A mixture of equal parts of glycerin and acetic acid is a very 

 convenient mounting medium for many kinds of tissue. Especially 

 is this true with some of the fungi. In the preparation of this 

 mixture, pure glycerin and concentrated acetic acid should be used. 



King's flounting Medium. 



This is good for many fresh- water algae, and like all fluid 

 mounts it must be used in a cell. It can be secured of dealers in 

 mici'oscopical supplies. 



Water. 



Water is not infrequently employed as a mounting fluid. To 

 preserve the mounts from deterioration a little camphor should be 

 added. Water is often used as a medium for the studying of fresh 

 tissue ; but it should be borne in mind, that it may change the 

 nature of the tissue materially, owing to the osmosis between the 

 cell contents and medium. This can be prevented by adding some 

 substance to the water to make its density equal to that of the tis- 

 sue, or cell contents. Salt is sometimes used, but is by no means 

 efficient. 



