242 The Microscope. 



copist is studying other objects, yet the effect is rarely employed. 

 In such cases, however, when the mirror is swung far to one 

 side, and the objective is not properly corrected, the result is 

 just about what Dr Frey calls it, truly diabolical. 



The Brownian movement or pedesis is that continuous quiver- 

 ing or dancing common to all minute particles when suspended 

 in water. It is not an evidence of life, and must not be mistaken, 

 as it is apt to be mistaken by the beginner, for minute living crea- 

 tures. It may be seen to good advantage by rubbing up a little 

 gamboge or carmine in water, allowing the larger parts to settle, 

 and then examining a drop of the supernatant liquid with a high 

 power objective. The field will be full of dancing and trembling 

 particles, moving irregularly but as if endowed with life. Simi- 

 lar movements are beautifully visible within certain Desmids 

 and Algse, especially if they are not in a healthy condition. The 

 minute black granules then hover together, and swing and quiver 

 like a swarm of microscopic bees. It is also noticeable within 

 the little sacs near the base of the spinal nerves of the common 

 frog, and in almost any place where finely divided matters are in 

 suspension. The cause of the movement is not known. An 

 explanation is that it is produced by currents of heat. How 

 long it lasts is not known. One writer claims to have prepared 

 a slide which he examined at the end of seven years and found 

 the particles as active as at first. Soap and water are said to 

 produce an energetic pedesis, and it is claimed that our hands 

 are cleansed as effectually by the violent pedetic movements of 

 the soap, as by its chemical action. In any event, do not mis- 

 take this uncertain dancing as seen under the microscope, for 

 the quivering of minute Bacteria or for other living plants or 

 animals. 



In addition to the three foregoing microscopical bug-bears, 

 ■which cease to terrify when well known, the student should 

 make himself familiar with the appearances of starch granules, 

 and with cotton, woolen and linen fibres, especially when colored, 

 as woolen fibres are apt to be if the work room is carpeted, as it 

 should not be. I can scarcely imagine an object any more 

 stonishing on first acquaintance than a purple fibre from the 

 arpet or elsewhere. These, with cotton and linen, are likely to 

 be found in any preparation ; even in mounted slides they are 

 common, having fallen into the mounting medium or been en- 



