80 CYTOLOGICAL TECHNIQUE 



gives good sections for electron-microscopy as well as for light- 

 microscopy. 



If the segmers of butyl methacrylate were only capable of 

 linking together in the way previously mentioned, the substance 

 produced would resemble a fibre rather than a resin. In fact, the 

 long chains branch and link in such a way as to form a three- 

 dimensional spongework devoid of any particular orientation. 

 The reactions involved in this process are mentioned below 

 (p. 82). It is this submicroscopic structure of the methacrylates 

 that fits them so well for use as embedding media, capable of 

 being sectioned equally well in any direction. 



At room-temperature the monomer very slowly undergoes 

 spontaneous polymerization. An inhibitor must be added to 

 enable the methacrylate to be stored in monomeric form. 

 Quinone is suitable. It is stated to react with chain-forming 

 radicles to produce stable compounds. ^^ Manufacturers add a 

 small proportion of hydroquinone to methacrylate, and this 



O 

 OH 



OH 



Hydroquinone 



becomes converted to quinone by spontaneous oxidation. When 

 the methacrylate is about to be used, the inhibitor is removed by 

 shaking the fluid with an aqueous solution of sodium hydroxide. 

 The water, coloured by the inhibitor, separates from the metha- 

 crylate under the influence of gravity. The monomer is washed 

 free from sodium hydroxide by being shaken several times with 

 distilled water; the latter is then removed by the addition of 

 anhydrous sodium sulphate. Although uninhibited, the material 

 will remain unpolymerized for many weeks if kept in a refrigerator 

 maintained near 0° C. 



The methacrylate is now ready to receive the tissue. The 

 molecules being fairly small, thorough penetration takes place 

 quite easily. The fluid is changed a few times to get rid of the 



