THE PREPARATION OF MICROSCOPICAL OBJECTS. 7 



1. Normal Salt Solution: a 0-75 per cent, solution of com- 

 mon salt in water. This is very useful in the examination of 

 fresh ^ specimens of animal tissues, as, unlike water, it has 

 practically no action on them. It cannot be used, however, 

 for making permanent preparations. 



2. Glycerine can be used either pure or diluted with its own 

 bulk of water. If the preparations are intended to be per- 

 manent, a narrow ring of cement must be painted round the 

 .edge of the cover-glass to fix it to the slide. 



3. Canada Balsam is the most generally useful, requiring no 

 cement. Specimens that are to be mounted in balsam must 

 iirst be deprived of all water they may contain by placing for 

 an hour or so in absolute alcohol, and should then, before 

 mounting, be soaked for a few minutes in oil of cloves or tur- 

 pentine in order to clear them, i.e., render them permeable by 

 the balsam. Canada balsam, if too thick, may be diluted with 

 chloroform, turpentine, or benzole. 



B. Teasing. 



_ The object of teasing is to separate the several parts of a 

 tissue or organ from one another in order to show their minute 

 structure. 



The fragment to be teased should be placed on a slide in a 

 drop of the medium in which it is to be mounted, and then 

 torn up into shreds by means of a couple of needles held one 

 ni each hand. The process is often greatly facilitated by 

 placing the slide on a piece of black paper, which renders the 

 particles easier to see. When torn up as finely as possible, a 

 cover-glass is placed on as before. The two rules to be borne 

 in mind in teasing are the following. 



1. Take a very small fragment to commence with. 



2. Tease it as finely as you can. Your object is to separate 

 the component parts from one another. 



C. Maceration. 



_ The process of teasing is in many cases facilitated by pre- 

 viously macerating the specimen, i.e., soaking it in some fluid, 

 which, while preserving the individual cells, tends to loosen 

 them from one another. The most important macerating fluids 

 are as follows. 



