134 APPENDIX 



on the mounting stand until the styrax bubbles and then allow to cool. If bubbles still 

 remain, heat again until they disappear. It is well to mount several slides more than 

 required, as some may be imperfect. 



Preparation of Selected Mounts. Take a slide, place a minute quantity of beeswax on 

 two places at a distance apart nearly equal to the diameter of the cover used. Place a 

 cover on the wax and press it down flat, or sufficiently to keep it in position. Dip a fine 

 needle into the following cement: 



Glacial acetic acid 12 drachms 



Gelatine 2 drachms 



Alcohol 1 drachm 



This is made by adding the acid to the gelatine in a water-bath and then the alcohol, and 

 filtering. Apply the moistened needle to the centre of the cover and spread as small a 

 quantity as possible in a thin layer. Now place the slide upon the turn table, centre it 

 with respect to the position of the gelatine, and with the finest sable brush draw a circle 

 about a tenth of an inch in diameter around the gelatine in water-color (Windsor), blue or 

 vermilion, or in India ink. Instead of the water-color, a circle of tin-foil the size of the 

 cover and pierced with a hole in the centre may be used, but the colored circle is to be pre- 

 ferred, as, when brought into view, it indicates exactly the focus required for observing 

 the diatom. 



The bottle containing the cleaned material, which has been kept in water and alcohol, 

 should be refilled with distilled water and well shaken, when a small portion may be taken 

 up with a dipping tube and evenly distributed over a portion of a slide and then dried. By 

 the use of a mechanical finger, fitted with a small piece of finely spun glass attached by 

 wax to the holder of the finger, when the microscope is focussed until the glass thread 

 touches the diatom selected, it will adhere to the thread. Raise the body of the micro- 

 scope, remove the slide containing the spread material, or move it to another part of the 

 stage, and place the slide with the prepared cover in the same position. Now carefully 

 lower the body-tube of the instrument until the diatom rests upon the gelatine, breathe 

 gently upon it, remove the cover from the slide, invert it over another slide containing a 

 drop of styrax and proceed by heating to mount as before. The size of the diatom, the 

 amount of gelatine, and several other factors, will enter into the question of success or 

 failure. I have, however, employed the above method and have mounted thousands of 

 slides of selected diatoms successfully. It is necessary to avoid any air current which 

 will cause the diatom to fall from the thread. On very cold days the glass thread some- 

 times becomes electrified and the diatoms will not stick; on sultry days in August hi our 

 locality the diatoms will stick too closely. 



By the same method, slides of arranged diatoms can be made using a glass circle 

 properly marked with lines in the eye-piece. Care should be taken to use glass threads 

 more or less in proportion to the size of the diatoms. A cat's whisker is preferred by some 

 to the glass thread. It has the advantage of not breaking, but unless it is quite short it is 

 too flexible. If the point of the thread becomes covered with gelatine, lower it into a minute 

 drop of water upon a separate slide, and by moving it about it will be cleaned. The diatom 

 itself may be washed in the same way, if it is not too small. 



Instruments Required. For collecting, in order to determine the quality of the find, 

 any simple lens of fifteen to twenty diameters is sufficient. A Stanhope is quite useful 



