20 THE ELEMENTS OF VEGETABLE HISTOLOGY 



before mounting specimens. These slips of giass are 

 usually covered with a film of dirt which cannot be 

 removed by simple polishing. They should be boiled 

 in water containing a trace of ammonia, transferred 

 to alcohol and dried with a silk or linen cloth. The 

 cleaning mixtures listed in the appendix are very 

 efficient. The use of cotton or woolen cloth for clean- 

 ing glassware or lenses is objectionable because of 

 the fibers which adhere to the glass and which may 

 be mistaken for parts of the specimen under exami- 

 nation. Clean slides and cover-slips should be kept 

 free from dust and handled only by their edges. Finger 

 prints which are almost invisible to the naked eye 

 are very apparent when highly magnified. 



MOUNTING MEDIA 



Mounting media are classified as temporary and 

 permanent. Temporary mounting media include fixed 

 oils, volatile oils, water, glycerin, chloral hydrate 

 solutions and alcohol. Mixtures of water and gly- 

 cerin with or without the addition of alcohol may often 

 be used to advantage. The oils and chloral hydrate 

 solution may be used in mounting specimens contain- 

 ing so much fatty material that cloudiness would 

 result from attempts to mix them with aqueous media. 

 Temporary mounts are well adapted to routine exam- 

 inations of food and drug samples, where preservation 

 of the specimen is not essential and where the work 

 upon a sample does not extend over too long a period 

 of time. Owing to evaporation of the medium, if 

 it be water or alcohol, or absorption of moisture if 

 it be glycerin, these temporary mounts cannot be 



