26 THE MICROSCOPE 



Foreign Bodies, etc.— 



In making microscopic preparations, certain foreign bodies 

 from time to time become present which it is necessary to care- 

 fully distinguish from the tissues under examination. The more 

 common of these should, therefore, be placed under the micro- 

 scope, and sketches made of them, in order that their characteris- 

 tics may be known. 



I. — Brownian* movement.— This vibratory movement should 

 be carefully distinguished from any vital one. Although it is 

 shown by some specimens of living matter, it is also observed in 

 ;^^;2-living matter, and is essentially a physical phenomenon. It 

 may be studied in — 



(a) Gamboge. — Grind some gamboge in water, and examine a 

 drop under the high power. Various currents will be detected, 

 and also this vibratory Brownian movement of the small granules. 



(b) Bacteria. — Mount a specimen from a watery extract of 

 boiled meat, which has been allowed to stand a few days. Some 

 very fine Bacteria will be seen which will show a similar motion, 

 and which lasts after their death, brought about by the addition of 

 iodine or by boiling the solution. Another way is to infuse some 

 hay in warm water for half-an-hour, filter, and set aside the fil- 

 trate ; note the changes which go on in it. At first, it will appear 

 clear ; in 24 or 36 hours, it will have become turbid ; later on, a 

 scum forms on the surface, and the infusion acquires a putrefac- 

 tive odour. Treat as above, with Iodine. 



2. — Cotton Fibres. — These are one of the pests of mounters. 

 Mount a few fibres of cotton wool in water, cover and examine 

 under both low and high powers. They appear as long, flat 

 threads with a distinct twist, and turn blue on the addition of 

 iodine and hydric sulphate. 



3. — Flax Fibres. — Examine in a similar manner some flax 

 fibres. These are long and flat, but, unlike cotton, do not show 

 any twist. 



4. — Air-Bubbles. — Shake a solution of gum in a test-tube till a 

 froth appears, then mount a drop of the under fluid, and examine 

 under both low and high powers. By transmitted light, each air- 



