188 CLEARING AGENTS. 



Rousseau, Paris. This sample was absolutely colourless. It 

 totally failed to clear absolute alcohol objects after many 

 days. 



The authors think that a laboratory supplied with cedar oil 

 and origanum oil is fully equipped for all possible cases (the 

 origanum oil being used merely to take the place of cedar- 

 wood oil for the special case of celloidin sections). See below, 

 335. 



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

 is one of the best media, if not the very best, for preparing 

 objects for paraffin imbedding. 



332. Clove Oil. Samples of clove oil of very different 

 shades of colour are met with in commerce. It is frequently 

 recommended that only the paler sorts should be employed 

 in histology. A word of explanation is here necessary. 

 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 substances in com- 

 merce. 



Two important properties of clove oil should be noticed 

 here. It 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 in. The second property I wish to call 

 attention to is that 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. 



Clove oil has, I fancy, the highest index of refraction of all 

 the usual clearing agents ; it clears objects more than balsam. 

 It dissolves celloidin (or collodion), and therefore should not 

 be used for clearing sections cut in that medium, without 

 special precautions. Notwithstanding the opinion of Schieffer- 

 decker, I consider this to be one of the best of clearing 

 agents, and very valuable on account of the properties, to 

 which attention has been called above. New clove oil washes 



