MICECfSCOPIO MANIPULATION. V73 



they should be covered with round or square pieces of very thin 

 glass, Tirth to Troth of an inch thick. The slides ought to he made 

 of thin plate-glass, and the covers of very thin crown or plate glass. 

 In examining recent vegetable structures, it is best to moisten 

 them with water. When the parts are dry, thin sections may be 

 made either by means of slicing instruments or by a sharp knife. 

 Many dry objects are well seen when immersed in Canada balsam. 

 To preserve objects in a moistened state, the substances used 

 are alcohol, a mixed solution of salt and alum and corrosive Sub- 

 limate, water containing a small quantity of creasote (five drops 

 to the ounce), and glycerine. The objects, in such instances, are 

 placed in shallow glass cells, or they are laid on the slides and covered 

 with thin glass, which is cemented by means of japanner's gold size, 

 or black japan varnish. The methods of procedure are afterwards 

 described. 



In proceeding to use the microscope it is necessary to have a 

 variety of tools and apparatus to aid in preparing objects for investi- 

 gation. These may be arranged beside the observer in such a way 

 that they shall be always within his reach.* A small tray or box, 

 with divisions, containing a pair of needles in handles (such as are 

 used for crotchet needles), a sharp knife or razor, a section-knife 

 (such as- that invented by Valentine, and which bears his name), 

 Scissors, and a pair of sharp or fine needle-pointed forceps, about three 

 inches long, are among the most essential instruments required. Glass 

 slides may be arranged also upon the same tray for common use, and 

 the thin glasses for covers should be kept in a small box by themselves. 

 In manipulating the object to be examined certain re-agents are re- 

 quired. These are : — 1. Distilled water. 2. Methylated alcohol un- 

 diluted, and also diluted in the proportion of about 1 part to 10 of 

 distilled water ; it is the best preserving agent ; it removes colour and 

 also air. 3. Ether, which dissolves resins, fats, and oUs. 4. A 

 solution of liquor potassse diluted to about 1 to 20 ; it swells up, 

 and sometimes separates membranes of cells and tubes when they 

 exist in condensed layers. 5. A solution of iodine in iodide of potas- 

 sium of the following strength — namely, 1 grain of iodine to 3 grains 

 of iodide of potassium, and an ounce of distilled water. 6. Chrolnic 

 acid diluted in the proportion of about 1 to 30 or 40 of distilled water. 

 The last two re-agents chiefly act by colouring the cell-waUs or the 

 <!ontents of the cells. 7. Sulphuric acid. 8. Oil, such as the finest 

 of that obtained from coal, and known as mineral oil, is to be recom- 

 mended for examining and preserving objects. It does not become 

 rancid, nor has it any afiBnity for oxygen. For the examination of 

 pollen and spores there is nothing better. 9. One part of dry calcium 



* The following details are partly condensed from Schacht's Treatise on the Mieroscope, 

 and from the works of Hannover, Quekett, Jabez Hogg, and Beale. 



