INTRODUCTION. 21 



and laid in oil of origanum cretici. This oil does not 

 dissolve the celloidin imbedding mass. As soon as 

 it becomes transparent, when it usually sinks to the 

 bottom of the dish, it is spread on a slide, the excess 

 of oil removed, a drop of balsam put upon it, and 

 covered by thin glass. This process, which seems at 

 first somewhat complicated, is readily understood, if 

 we remember that neither the water in which the 

 specimen usually lies when the staining is completed, 

 nor the alcohol, which, being hygroscopic, removes 

 the water, are miscible with balsam ; and further, 

 that alcohol is miscible with oil of origanum, and oil 

 of origanum with balsam. Care must be taken in 

 these manipulations not to breathe on the specimen, 

 nor to allow any moisture to come in contact with 

 it, since even a small amount of moisture produces 

 a precipitate in the balsam which greatly diminishes 

 the clearness of the preparation. Canada balsam is, 

 as a rule, best adapted for mounting those specimens 

 in which we wish to study the general structure of a 

 tissue rather than its more minute characters. Prep- 

 arations in which the blood- or lymph-vessels are 

 injected with some colored material usually show 

 best when mounted in balsam. 



To make the double staining with haematoxylin 

 and eosin, as mentioned above, we may first stain in 

 the usual way with an aqueous solution of haema- 

 toxylin, and then accomplish the eosin staining by 

 adding a few drops of a saturated solution of eosin 



