FRENZEL'S GUM METHOD. 217 



It has been stated (VossELER, Zeit.f. wiss. Mik., vii, 4, 1891, 

 p. 457) that Mayer's albumen generally "goes bad," and 

 loses its adhesive power after about six months' keeping. 

 The only remedy for this is to make up fresh mixture every 

 few months, as no change of antiseptics has had any effect in 

 improving its keeping qualities. 



329. Flogel's Gum Method (Zool. Anz., 1883, p. 565). Make 

 a solution of one part gum arabic in twenty parts water, filter, 

 and add a little alcohol to prevent the formation of mould. 

 Slides are prepared by pouring the solution over them, and 

 draining. (It is important that the slides be so perfectly 

 clean as to be evenly wetted all over by the gum solution.) 

 Sections may now be cut and laid on the gum surface before 

 it has become dry, and floated into the proper position ; this 

 is the best plan for sections of y^- mm. thickness, and for 

 large sections. For thinner and small sections it is best to 

 take slides that have completely dried, arrange the sections 

 dry on the gum film, and then breathe on it until the gum has 

 become sticky. 



A very neat method for cases in which it is not required to 

 treat the slide with watery fluids. 



WADDINGTON (Journ. Quek. M. Club, vi, 1881, p. 199 ; Journ. Roy. Mic. 

 Soc. [N.S.], i, 1881, p. 704) gives the following process for preparing 

 " arabin," a purified gum arabic which lias the advantage of not presenting 

 a granular appearance under the microscope as ordinary gum arabic does. 



Dissolve clear and white gum arabic in distilled water to the consistency 

 of thin mucilage. Filter. Pour the filtrate into rectified alcohol, and si mice 

 well ; the arabin separates as a white pasty mass. Place it on filter-paper, 

 and wash with pure alcohol until the washings are free from water. Dry. 



The white powder thus obtained should be dissolved in distilled water and 

 filtered twice. It may then be placed on slides, which are drained, dried, 

 and put away till wanted. In this condition it may be preserved indefinitely. 



330. Frenzel's Gum Method (Arch. f. mik. Anat., Bd. xxv, 

 1885, p. 51). Gum arabic is dissolved in water to the consist- 

 ency of a thin mucilage, and to this is added aqueous solution 

 of chrome-alum. An excess of the latter does no harm. 

 Finally add a little glycerin and a trace of alcohol (1. c., p. 142) . 

 The slide is prepared with this in the usual way, the sections 

 (either cut dry or in the wet way) are gently pressed on to it 

 with a brush and slightly melted on, and heated for at most a, 

 quarter of an hour at a temperature of 30 to 45 C., which 



