1899] MICROSCOPICAL JOURNAL l25 



lution (1:2), and I cc. concentrated alcoholic solution of 

 fuchsin. Stir the mixture, filter, reject the filtered pre- 

 cipitate and keep the fluid which improves as time elapses. 

 This constitutes a mordant which has aflBnity both for 

 the organism and for the dye which is to follow. Wet 

 the fixed specimen in it after having first moistened it 

 with water, gently heat over a flame till vapor comes off 

 but without boiling. After 60 or 90 seconds wash it 

 thoroughly in water to take off all the mixture from the 

 glass which will occur if the heat has not been too intense. 

 If it has been, scrape off the debris from the glass to 

 make it perfectly clean for by the dye which is to follow 

 the glass would be badly disfigured if a mordant base re- 

 mained on it. The dye now follows. It consists of a 

 one-to-fifty-part hot aqueous saturated solution of 

 fuchsin, or ofa solution made by heating 3 grams fuchsin 

 in 100 cc. anilin water. Moisten the surface of the 

 mordanted specimen with it, heat over the flame and wash 

 as above directed. This dye gives colored flagella or a 

 colorless back ground visible under a 1-12 inch homoge- 

 neous oil imm. objective if the manipulations have been 

 skillfully made. 



LETTERS TO THE EDITOR. 



GATES' DOUBLE MICROSCOPE. 



Defining Power. — According to Abbe's theory, gener- 

 ally accepted by microscopists, defining power is purely a 

 function of numerical aperture, and if, as Dr, Gates claims, 

 he has really succeeded in seeing detail with a combination 

 of dry objectives, which oil-immersion objectives of high 

 aperture employed in the usual manner fail to show, all 

 Abbe's theories must fall to the ground. It is rather sig- 

 nificant, though, that in spite of the enormous advances he 

 claims to have made, no detail of any new discovery, such 

 as the minute structure of diatoms, for example, are indi- 

 cated. Even if some new structure were apparently ex- 



