THE MICROSCOPE. oo 
In this manner, vacuoles can be distinguished from oil- 
globules in the bodies of the infusoria, &c., and tubes can 
be distinguished from solid rods. 
EXERCISE V. 
a. Mix a little indigo from a water-colour box in water, 
put a drop on a slide, and cover. Examine with 
your highest power, the deepest eye-piece, and the 
draw-tube pulled out. Notice the smaller particles 
of the paint. They will be seen to have a jerky, 
dancing kind of movement in no one particular 
direction. These movements are called “ Brownian 
movements ;’ they will go on for ever, provided the 
slide does not dry up. The cause is purely physical, 
probably the mutual transference of heat between 
the particles and the water. It must be carefully 
noticed, so as not to mistake it for vital movement. 
EXERCISE VI. 
a. Place a small piece of sea-weed in a wine-glass of salt 
water, and let it remain two or three days until it 
begins to decompose. Place a very small fragment 
on a slide with a drop of the water it was in; tease 
it out with needles, and put on a cover-glass. 
b, Examine first with the inch objective, and then with 
the quarter*. Numerous infusorians will be seen 
swimming about by means of their cilia. 
* In almost all cases an object should be examined with a low power 
before looking at it with a high power. Not only is the general form and. 
structure better made out with a low power, but portions may be selected. 
D 
