riiAPTMU vr. 



that clearing be done, whenever possible, in shallow corked 

 tulrs, under which conditions the phenomenon rarely occurs. 

 In any case, be careful not to breathe on the liquid. 



120. Choice of a De-alcoholisation or Clearing Agent. I 

 advise the beginner to keep on his table the following : 

 Oil of cedar, for general use and for preparing objects for 

 imbedding in paraffin ; clove oil for making minute dissec- 

 tions in ( 122), and for much work with safranin, etc.; oil 

 of bergamot, which will clear from 90 per cent, alcohol, and 

 which does not extract coal-tar colours ; carbolic acid, for 

 rapidly clearing very imperfectly dehydrated objects. 



For special clearers for celloidin sections see Chapter IX. 



121. Cedar Oil (NEELSEN and SCHIEFFERDECKER, loc. cit., 

 118). Clears readily tissues in 95 per cent, alcohol with- 

 out xhrinkage ; does not extract anilin colours. Celloidin 

 sections are cleared in five to six hours. 



The observer should be careful as to the quality of the 

 cedar oil he obtains. I have examined the clearing proper- 

 ties 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 my experience, the very best of all media for 

 preparing objects for paraffin imbedding. I find it to be /r.v.s 

 hurtful to cells than any other medium known tome. Tissues 

 may remain in it for any length of time without hurt. If it 

 should become milky through keeping, filter. 



122. 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. 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 ;m 

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

 substances in commerce. 



Clove oil does not easily spread itself over the sin-face of 



