AND HOW TO USE IT. 25 



limited. For general use, we strongly advise the student to' 

 purchase the freezing microtome, as it will be found much 

 more efficient. A dozen porcelain paint-saucers or watch- 

 glasses, camel-hair pencils ; sUdes, covers (both square and round), 

 and a bull's-eye side-condenser. This last accessory we have so 

 seldom used, that when we have required one we have filled a 

 clear white glass bottle with water, and fastened it between the 

 lamp and the object, when it has proved almost as efficient as the 

 bull's eye ; but where the student is giving his attention more par- 

 ticularly to opaque objects (Foraminifera, etc.), he will find the 

 bull's-eye condenser very serviceable. A small paraffin oil lamp 

 with a white paper shade is very useful for winter-evening work ; 

 Canada Balsam and Benzole, Glycerine Jelly, and various stains 

 and cements. Experience will best teach what stains and cements 

 are most required, and these it will be best to purchase as needed, 

 as it will depend on the class of work. 



In studying the microscopic structure of various bodies, it is 

 necessary to add different reagents and staining fluids. Fre- 

 quently, it is best to put up the object and then add the fluid, 

 which may be done : — {a) By the use of a glass rod or blotting- 

 paper ; or {b) by using the rod and a fine capillary tube. 



Testing. — By using reagents in the above manner, many sub- 

 stances may be detected under the microscope by certain charac- 

 teristic reactions. As examples of this, the reactions of starch and 

 cellulose may be mentioned. 



Starch. — Mount a few granules of starch by mixing some 

 in cold water and covering a drop upon a slide. Examine under 

 a high power. Now add by capillary attraction a dilute solution 

 of Iodine, and the granules will turn blue ; this is a well-known 

 and characteristic reaction. 



Cellulose. — Mount some scrapings from the cut surface of a 

 potato. Examine under a high power, and run in a little Iodine 

 solution ; the starch-granules present turn blue, and the walls of 

 the cell-spaces containing them take a yellow tint. If, in a similar 

 manner, dilute hydric sulphate be now added, this yellow tint will 

 change to a blue one, indicating cellulose. The same reaction is 

 given by cotton fibres, or the walls of yeast-cells. 



