72 DE-ALC0H0LI8ATI0N AND CLEARING 



Xylol is the clearing agent in most common use at present. It 

 will mix with 95 per cent, alcohol, but it is advisable to pass 

 objects through absolute alcohol in order to ensure complete 

 dehydration. Xylol has a tendency to harden all tissues, if they 

 are left in it too long, and yolk ladened tissues are rendered 

 especially hard and brittle. For tile latter one should use either 

 some other clearing agent, described below, or some measure for 

 keeping the tissue soft (see § 138). 



Both xylol and toluol are liable to become acid if kept too long 

 in partially filled vessels. To remove water from cheap xylol 

 suspend a bag of fused copper sulphate in the jar. 



152a. Carbol-xylol. In moist localities it is often difficult to 

 clear alcoholic material with xylol alone and carbol-xylol must be 

 used. (Made by adding anhydrous crystals of pure phenol to 

 xylol until no more will dissolve.) After clearing the object can 

 be rinsed in pure xylol, if desired. 



Some workers prefer a mixture of equal parts of xylol and 

 beechwood creosote for clearing. 



153. Normal Butyl Alcohol. The use of this reagent as a dehydrating 

 and clearing fluid is relatively new. It was first suggested, apparently 

 by Mile. Larbaud (Comp. Rend. Acad. ScL, 172, 1921, p. 1317), but 

 was brought to the fore by Zirkle (Science, Ixxi, 1930, p. 103), who 

 uses and recommends it for woody tissues which are rendered too hard 

 and brittle for cutting after ethyl alcohol-xylol treatment. More 

 recently, it has been found valuable for animal tissues as well, especially 

 for lightly chitinised insects which must be sectioned (Stiles, Stain 

 Tech., 9, 1934, p. 97). The advantages claimed for n-butyl alcohol are 

 that the hardening effects of higher grades of ethyl alcohol and xylol 

 are avoided by its use, and a long time may be taken for dehydration 

 and clearing without any deleterious effect upon the tissue. On the 

 other hand, it requires four or five days to infiltrate tissue with paraffin 

 by this method, a fact which may restrict its use. For a detailed 

 description of the method see §§ 127 and 1257. 



154. Isopropyl Alcohol. Bradbury (Science, Ixxiv, 1931, p. 225) has 

 used isopropyl alcohol as a substitute for ethyl alcohol, the main 

 advantage being that the former does not harden tissue as much and 

 makes the sectioning of much material easier. (See also § 128.) 



