MICROTECHNICAL METHODS 

 CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 20 3 

 W. J. G. Land 

 An improved method of replacing the paraffin solvent 

 with paraffin 

 In paraffin imbedding the almost universal custom when repla- 

 cing a paraffin solvent with paraffin is to add from time to time small 

 pieces of paraffin to the solvent, until at room temperature no more 

 paraffin is dissolved. Then the container is either placed in a low 

 temperature oven or on an oven of higher temperature and paraffin 

 added until the new saturation point is reached. The container is 

 then placed in an oven having a temperature one or two degrees 

 above the melting point of the paraffin and more paraffin is added. 

 When the last paraffin has melted the mixture is poured off and 

 replaced with pure melted paraffin. The object in repeatedly add- 

 ing small quantities of paraffin is to prevent a too rapid increase in 

 the density of the xylol-paraffin or whatever solvent is used for 



paraffin. 



Objects to be imbedded, being heavier than xylol, sink to the 

 bottom. Paraffin, which is heavier than xylol, also sinks, with the 

 result that the objects are almost immediately surrounded by a 

 dense layer of dissolved paraffin, thereby defeating the end sought 

 by a gradual addition of paraffin. It has repeatedly come to the 

 notice of the writer that much of the damage to delicate plant tissues 

 takes place during the replacement of the solvent by paraffin. 

 Many otherwise careful workers are particularly careless at this 



point. 



In order to prevent the object from coming into immediate con- 

 tact with the dense xylol-paraffin solution, a piece of wire gauze is 

 bent in such a manner that it forms a support 2-3 cm. above the 

 object, and xylol sufficient to rise 1-2 mm. above the support is 

 added. The container (a shell or bottle) is then tilled with blocks 



, [Botanical Gazette, vol. 59 



