74 CYTOLOGICAL TECHNIQUE 



this substance to ethylene glycol (the familiar 'anti-freeze') is 

 shown by the structural formulae. It is made by the action of 



HO— CH2 



C0H50— CH2 



Cellosolve 



ethanol on ethylene oxide under pressure at high temperature. 

 It is a colourless, odourless liquid boiling at 134°C.^°^ It has 

 remarkable powers of dissolving diverse substances, including 

 cellulose nitrate and acetate (whence, presumably, its trade name). 

 It is miscible with water and with toluene in all proportions. 



Since cellosolve is a less violent dehydrating agent than ethanol, 

 there is no advantage in using a graded series of mixtures of 

 cellosolve with water. Fixed tissues may be transferred from water 

 to a mixture of cellosolve with an equal volume of water, and 

 then to absolute cellosolve; indeed, it is possible to omit the 

 intermediate stage. If the fixative contained mercuric chloride, 

 iodine should be dissolved at 0-5% in the cellosolve; it must 

 subsequently be washed out by the pure solvent. Tissues pass 

 from absolute cellosolve to a mixture of this with an equal volume 

 of toluene, and thence to toluene itself. 



Cellosolve causes less shrinkage and hardening than ethanol. 

 Indeed, there are some organs, such as mucous glands, that can 

 scarcely be sectioned in paraffin after dehydration by ethanol, 

 but present no difficulty when cellosolve is used instead. The 

 great solvent power of this substance is, however, a drawback for 

 certain kinds of work. It appears to dissolve some of the con- 

 stituents of mitochondria, even when appropriate fixatives have 

 been used.^^ In studies of cytoplasmic inclusions it is safer to pass 

 tissues through ethanol, unless it has been shown that the use 

 of cellosolve is not harmful. 



Tissues may be transferred directly from toluene to melted 

 paraffin. It would not appear that there is any advantage in 

 soaking them first in a solution of paraffin in the antemedium.'^ 



Paraffin waxes are constituents of crude petroleum. They are 

 saturated, long-chain hydrocarbons of the methane series. The 



