20 NORMAL HISTOLOGY. 



when the direction is given to " stain a specimen 

 double," this use of haematoxylin and eosin is to be 

 understood. 



The most convenient way of using Canada balsam 

 is in solution of oil of cedar. The commercial bal- 

 sam is evaporated, at a gentle heat, until it becomes, 

 upon cooling, hard and brittle like glass. This hard 

 balsam is dissolved in oil of cedar, making a solution 

 of such a consistency that it will drop readily from 

 the end of a glass rod. The solution may be kept in 

 glass-capped wide-mouthed bottles, or in artists* color 

 tubes. The mode of procedure in Canada-balsam 

 mounting is the following : The specimen having 

 been suitably prepared and stained, it is freed as 

 completely as possible from water by touching its 

 edges with a bit of filter paper, and then placed in a 

 small wide-mouthed bottle containing a few cubic 

 centimetres of common strong alcohol ; after from ten 

 to fifteen minutes it is transferred to absolute alcohol* 

 where it remains fifteen minutes. It is then taken 

 out, the superfluous alcohol removed by filter paper, 



* Alcohol that will answer for this purpose can be prepared as fol- 

 lows : Fill a wide-mouthed bottle, holding about a litre, three quar- 

 ters full with strong alcohol. Pulverize a quantity of cupric sulphate 

 and heat until the water of crystallization is driven off and the powder 

 becomes almost perfectly white. When cold, pour into the alcohol 

 and shake. Anhydrous cupric sulphate is insoluble in alcohol, but 

 takes up the water contained in it. The 97 % alcohol of commerce 

 will answer for dehydration in place of absolute alcohol, although the 

 latter is preferable. 



