THE MICROSCOPE. ol 
EXERCISE IT. 
a. Place a small quantity of fine bread crumbs on to a 
dry slide, and examine with alow power. Not much 
will be seen, the crumbs looking black. 
b. Remove the slide from the stage; put a drop of water 
on to the crumbs; cover with thin glass; gently 
press the cover down with the handle of a needle; 
take up the surplus water. Examine with the same 
power as before. The bread crumbs will be found to 
be more or less transparent, their shape can be easily 
made out, and numerous starch granules will be seen 
floating about in the water. The reason the bread 
crumbs can be seen better in water than in air, is 
because the refractive power of water approaches 
nearer to that of starch. Almost all transparent 
objects are seen better in fluid than when dry. , 
EXERCISE III. 
a. Take the head of a fly and put it onaslide dry. Place 
the body of the microscope perpendicular, and close 
the diaphragm plate. Place the slide on the stage, 
and, if working by artificial light, throw a beam on 
to the fly’s head with the bull’s-eye condenser. Ex- 
amine with the low power. 
b. Take up the head of the fly in a pair of forceps; dip 
it in water, and replace on the stage. Examine it 
with the low power. Nothing can be made out, 
owing to the wet surface of the object reflecting the 
light, An opaque object should therefore always be 
examined quite dry. 
