14 BOTANICAL MICROTECHNIQUE. 



(b) The Replacement of Alcohol. 



18. In earlier years clove-oil was almost exclusively used 

 for the replacement of alcohol, and it is in many cases very 

 well adapted for that use on account of its complete misci- 

 bility with alcohol. For microtome sections fastened on 

 the slide it is sufficient to place a few drops of clove-oil on 

 the slide after the removal of the alcohol. Thicker sections, 

 especially free-hand sections, are best placed in a vessel with 

 clove-oil, in which they are left until they are completely 

 transparent and no longer appear white on a dark ground. 



But clove-oil has the disadvantage of washing out many 

 stains, and has been at present wholly given up by many 

 microscopists, on account of its oxidizing characteristics. 

 How far the other ethereal oils proposed as substitutes for 

 it oil of origanum, oil of lavender, and others are free from 

 these disadvantages remains to be discovered. 



19. But in any event we have in xylol a reagent which can 

 very well replace clove-oil. With microtome sections I use 

 it now exclusively except where I wish to utilize the differ- 

 entiating effect of clove-oil, as, for instance, in Gram's 

 method (321). 



Xylol has only the disadvantage that it mixes with alcohol 

 less readily and requires a more complete dehydration than 

 clove-oil. In consequence of this one easily finds milky 

 cloudings, and with thicker sections would better use, 

 between the alcohol and the xylol, a mixture of three vol- 

 umes of xylol and one volume of alcohol. For microtome 

 sections it is sufficient in most cases, on the other hand, to 

 cover them with the ordinary so-called absolute alcohol (98$) 

 and then to add xylol. The beginner will do well before 

 the final enclosure in Canada balsam to always examine the 

 preparations on a dark ground. If they appear white and 

 opaque, alcohol should be added again, and then xylol again, 

 until the preparations have become completely transparent. 



I will remark here that in this case, and in general when it 

 is desired to bring somewhat large quantities of fluid upon 



