14 INTRODUCTORY EXERCISES. 



the place of the alcohol. Observe this taking place under a low power. 

 Should there be any trace of opacity left it is due to incomplete 

 removal of water. Further treatment with alcohol is necessary and 

 clearing must again be performed, and if then there are no signs of 

 opacity, permanent mounting in balsam is finally performed by removing 

 superfluous essential oil with blotting paper, adding a drop of balsam 

 and covering. 



Examine with a high power (//) and observe the polygonal 

 cells joined edge to edge into a continuous sheet, each with a 

 violet stained nucleus. Two or three layers of cells may be 

 found superposed upon each other. 



Stain another piece with Piepoeapmine by covering it with a 

 pool of the reagent, give the stain five minntes to penetrate, remove 

 the excess with blotting paper, and apply Glycepin or Fappant, 

 just enough to fill the interval between slide and cover. As the 

 carmine effect does not develop for some time, it is necessary to 

 leave some of the stain in the preparation, which will become more 

 differentiated by the selective activity of the tissues in the course of 

 a week. Picrocarmine is a double stain, the carmine colouring the 

 nuclei arid connective tissue where such is present pink, and other 

 parts yellow. 



Mounting- sections of tissues cut in paraflin and which are 

 still permeated by the paraffin in which they have been embedded. 



As in the sequel the majority of the sections given out to 

 the class will be of this nature, the student should note care- 

 fully the uses of the following alternative methods. 



1. Simple treatment. If the section he flat, i.e., is riot curled or 

 crumpled beyond a very slight extent, and its parts do not tend to 

 fall asunder when the support of the paraffin is removed, proceed as 

 follows : Place the section in the centre of the slide, warm its under- 

 side over the burner just sufficiently to melt the paraffin and wash the 

 latter away with five or six successive drops of turpentine or toluene, 

 giving each drop time to act. In warming over the burner care must 

 be taken not to overheat or the tissue will be spoilt. The thickness 

 of the slide affects the time which the heat takes to reach the film of 

 paraffin, therefore pass the slide twice immediately over the flame and 

 wait a few moments to see if the paraffin is going to melt, testing the 

 temperature of the slide meanwhile on the back of the hand for future 



