20 



THE ART OF MAKING MICROSCOPE SLIDES 



Foraminifera 



Each drop of tragacanth should be slightly 

 smaller, both in breadth and in thickness, 

 than the test which is going to be placed 

 on it. These drops of mucilage are most 

 conveniently placed in the correct position 

 with the aid of a binocular dissecting 

 microscope. 



As soon as the drops have been placed 

 the slide is pushed out of the field of the 

 dissecting microscope and the watch glass, 

 containing the specimens to be mounted, 

 pushed into the field. A clean sable brush 

 is then moistened with the lips. It should 

 be sufficiently wet to cause the tip of the 

 brush to come to a point but not suf- 

 ficiently impregnated with saliva for any 

 liquid to be showing. The tip of this brush 

 is touched down onto the required speci- 

 men and held in the field of the dissecting 

 microscope with the right hand, while the 

 left hand pushes the watch glass of speci- 

 mens out of place and replaces the glass 

 slide. It cannot be emphasized too much 

 that the paper must be liberally moistened 

 or the drops of gum tragacanth will dry 

 in the period of time that it takes to 

 select tests. If, when the cell is replaced 

 under the binocular microscope, it is ob- 

 served that the mucilage is dry, do not at- 

 tempt to remoisten it; place another drop 

 of mucilage on top of the dry portion. 

 The shell, on the tip of the fine brush, is 

 now pressed down in the selected position. 

 If it is not exactly as required, it may be 

 adjusted with the tip of a needle. After 

 aU the tests required on any one slide 

 have been placed in position, a fine sable 

 brush is used to place a drop of water on 

 top of each shell. This makes certain that 

 there will be a perfect adhesion of the shell 

 to the underlying mucilage. 



On a very dry day (that is, one on which 

 the relative humidity is below 20%) the 

 preparations may be sealed immediately; 

 on humid days it is best to place the shdes 

 in a desiccator overnight. In either case, 

 the next step is simple. The top of each 

 cell is spread with a very thin coat of gold 

 size and a clean coverslip dropped into 

 position. It is best to place one edge of 

 the coverslip down first, supporting the 

 other edge with a needle, and then to lower 

 it by withdrawing the needle. As soon as 

 it is in contact with the cell it is pressed 



down all round its circumference with a 

 needle. It is not important that it should 

 be in contact all over since further coats of 

 cement will be placed on top. The initial 

 coat of gold size is intended only to hold 

 the coverslip in position through the next 

 stages and it is better to have a very thin 

 coat with an imperfect adhesion than to 

 have a coat so thick that cement spreads 

 onto the inner surface of the covershp. 

 The slides, with their attached covers, are 

 then placed on one side, preferably in a 

 desiccator, for a period of about 24 hours 

 to set the gold size. The shde is finished 

 on a turntable (Fig. 7) by turning onto 

 the upper surface of the cell a coat of any 

 selected cement. The author prefers either 

 asphalt varnish, or Brunswick black, 

 though any tough and flexible cement may 

 be used. It is quite important that the cell 

 should be accurately centered on the 

 turntable, and though this may be roughly 

 done with the aid of the concentric circles 

 engraved on the table, it is usually neces- 

 sary to spin it once or twice and to make 

 necessary adjustments manually. If lack 

 of experience renders this difficult, it is 

 suggested that a needle should be held 

 stationary above the edge of the cell and 

 the turntable rotated slowly. The table 

 should be stopped when the edge of the 

 cell (presuming it to be eccentrically 

 placed) is at the maximum possible dis- 

 tance from the needle. The cell is then 

 pushed one half of this distance towards 

 the needle, the needle replaced over the 

 edge of the shde, turned as before, and 

 readjusted. By this method even the most 

 inexperienced can center a cell perfectly 

 within a few moments. Only one coat of 

 varnish is really necessary, though some 

 people prefer to put on four or five, using 

 the last coats to fill up the edge of the 

 cell which is thus doubly protected. In 

 the author's opinion this is not necessary 

 and makes a clumsy mount. 



If, through accident, a test becomes 

 detached in one of these slides it may be 

 repaired easily. The coverslip should be 

 broken by a sharp blow with the handle of 

 a scalpel and the pieces removed with a 

 pair of forceps. The top of the cell is then 

 scraped clean with a scalpel and the test 

 recemented in place. 



