222 THE AMERICAN MONTHLY [Dec 



Practical Suggestions. 



By Iv. a. WILIvSON, 



CLEVEIyAND, OHIO. 



Flagellum of Ceratium. — The flagellum of this 

 animal when present is easily and plainly visible under 

 an ordinary and inexpensive one-quarter-inch objective. 

 It needs no staining nor a high angled expensive lens. 

 The flagellum is seldom seen as the little animals are 

 quite timid and at the slightest alarm retract this inter- 

 esting appendage. It has been suggested that the ani- 

 mals pass into a "still condition" and in that state re- 

 tract the flagellum. 



Flagellum of Bacteria. — These illusive organs may 

 be plainly and comfortably viewed vi^ith a cheap one-fifth 

 when properly stained. The difiiculty in demonstrating 

 these minute organs lies not with the lens but with the 

 lack of skill and technical knowledge in the method of 

 staining. To stain them requires experience, technical 

 knowledge and special skill. 



Gum for Fixing Objects to a Slide. — Selected pieces 

 of gum arable are dissolved in distilled water, so as to 

 form a thin mucilage. This is filtered, and the filtrate 

 poured into a considerable volume of alcohol, which pre- 

 cipitates the arable. This is separated from the mother 

 liquor by filtration, washed with alcohol and finally 

 dried. It is freely soluble in water and can be used in- 

 stead of the ordinary gum with advantage. It will ob- 

 viate the granular appearance of the gum when used to 

 fix objects to a slide. 



Blackening the Inside of a Draw-tube. — :Many 

 fine instruments are sold with the inside of the draw- 

 tube covered by a bright metallic surface. With such 

 an instrument it is impossible to obtain good photomic- 

 rographs or even to obtain a good defiinition. The fol- 

 lowing is a process for obtaining a dead black surface on 



