26 Botanical Microtechnique 



for very small or thin pieces to 3 hr. or more for large pieces of tissue. 

 A similar acetone-xylene series can be used. 



Chloroform may be substituted for xylene in a similar series, 

 except that more abrupt changes are permissible. A practical series is 

 as follows: 



(1) Vs chloroform 



-/i absolute alcohol 



(2) % chloroform 



Vs absolute alcohol 

 (S) Pure chloroform, changed at least once 



Chloroform does not make tissues as brittle as does xylene. 



Trichloroethylcne is a good solvent of paraffin and may be sub- 

 stituted for xylene in the foregoing processes. Trichloroethylcne is not 

 inflannnable and is not toxic unless inhaled directly in large qtianti- 

 ties. It dissolves Canada balsam but docs not affect stained sections. 

 This reagent deserves thorough trial with a wide range of subjects. 

 Any reagent that decreases the hazards of fire and ]:)oisoning is Avorth 

 serious consideration. 



Cedar oil is an excellent clearing agent after delnchation in 

 ethyl alcohol. The procedure is to pom a layer of cedar oil into 

 a dry vial, then carefully ])our the anhydrous alcohol containing the 

 material over the cedar oil. The pieces gradually sink into the oil 

 and become strikingly clear. The alcohol is removed \\ith a ])ipette, 

 and the cedar oil is rinsed out of the tissties \\ith several changes of 

 xylene. 



Recognition of the fact that the transparency of the tissues at this 

 stage of the j^rocess is of no value, and the widespread use of the 

 higher alcohols for dch\xlration and as wax sohcnts. ha\c' jiractically 

 eliminated the use of dealing oils. 



Following dehydration in any of the bui\l alcohols or dioxan, 

 no clearing reagent is used, because these reagents are sohents of 

 paraffin. They do not render the tissues appreciably transparent. 



Dehydration in Solvents of ParafFin 



THE BUTYL ALCOHOL METHOD 



Normal and tertiary buixl al(()li()l lia\t \kvu iniroduced into 

 microtechni(jue in recent years and show nuuh piomise as dehy- 

 drating and infiltrating agents. Normal l)utyl alcohol, also designated 

 butanol, was the first of these iiigher alcohols to l)i' used extensively. 

 Lang's careful experiments ha\e shown thai a miscibility curve of 

 the three components of the dehydrant may be used to ascertain the 



