DE-ALCOHOLISATION AND CLEARING 69 



136. Clearing Whole Mounts of Fresh-Water Micro-Fauna. 



Peter Gray (Watson's Microscope Record, No. 37, 1936), remarks : 

 Clove oil is rapid, but makes objects brittle ; terpineol is cheaper, 

 safer, pleasanter, but much slower. Beechwood creosote (B.P.) 

 is probably the best all round reagent, it clears imperfectly 

 dehydrated objects gently and effectively, leaving them flexible. 

 Do not use cedarwood oil, xylol or methyl salicylate, as these 

 need more perfect dehydration. 



For special clearers for celloidin sections see Chapter X. 



137. Cedar Oil (Neelsen and Schiefferdecker, loc. cit., 

 § 133). Clears readily tissues in 95 per cent, alcohol without 

 shrinkage ; does not extract anilin colours. Celloidin sections are 

 cleared in five to six hours. 



The observer should he careful as to the quality of the cedar oil he obtains. 

 We have examined the clearing properties of a sample, obtained from a 

 celebrated firm, which totally failed to clear absolute alcohol objects 

 after many days. 



Cedar oil is very penetrating, and for this and other reasons is, in our 

 experience, the very best of all media for preparing objects for paraffin 

 imbedding. We find it to be less hurtful to cells than any other medium 

 known to us. Tissues may remain in it for any length of time without 

 hurt. If it should become milky through keeping, filter. 



Cedar oil has been largely superseded by methyl benzoate (§ 131). 



138. Clove Oil. Samples of clove oil of very different shades 

 of colour are met with in commerce. It is frequently recom- 

 mended that only the paler sorts should be employed in histology. 

 Doubtless it is, in general, best to use a pale oil, provided it be 

 pure ; but it is not always easy to obtain a light-coloured oil that 

 is pure. Clove oil passes very readily from yellow to brown with 

 age, so that in choosing a colourless sample you run great risk of 

 obtaining an adulterated sample, for clove oil is one of the most 

 adulterated oils in commerce. 



Clove oil does not easily spread itself over the surface of a slide, 

 but has a tendency to form very convex drops. This property 

 makes it a very convenient medium for making minute dissections. 

 It also has the property of making tissues that have lain in it 

 for some time very brittle. This brittleness is also sometimes very 

 helpful in minute dissections. 



These qualities may be counteracted if desired by mixing the 

 clove oil with bergamot oil. 



This is one of the most useful of clearers. According to Behrens 

 {Tabellen, 3rd ed., 1898, p. 33), it will clear from alcohol of 74 per 

 cent. 



It has a high index of refraction, and clears objects more than 

 balsam mounting media. It dissolves celloidin (or collodion), and 

 therefore should not be used for clearing sections cut in that 

 medium without special precautions. New clove oil washes out 

 basic tar colours more quickly than old. 



