STAINING OF FLAG ELL A. 105 



Make a film as above described, and holding the cover- 

 glass in a pair of forceps, pour on as much of the mordant 

 A as the cover-glass will hold. Heat it carefully above a 

 flame till steam begins to rise and then move the prepara- 

 tion gently in and out of the hot-air column over the 

 flame for about a minute. Wash well in distilled water till 

 every trace of mordant appears to be gone. If necessary, 

 wash with absolute alcohol till only the film itself appears 

 tinted violet with the mordant. Filter a few drops of stain 

 B on to the cover, again heat till steam rises and leave in 

 the warm stain for one minute. Wash well in distilled 

 water, dry, and mount in xylol balsam. 



2. Van Ermengems Method for Staining FlageUa. 



The films are prepared as above described. Three solutions are 

 here necessary : 



Solution A. (Bain fixateur) 



Osmic acid, 2 per cent solution . . I part 



Tannin, 10-25 per cent solution . . .2 parts 



Place the films in this for one hour at room temperature, or heat 

 over a flame till steam rises, and keep in the hot stain for five minutes. 

 Wash with distilled water, then with absolute alcohol for three to four 

 minutes, and again in distilled water, and treat with 



Solution B. (Bain sensibilisateur] 



.5 per cent solution of nitrate of silver in distilled water. Allow 

 films to be in this a few seconds. Then without washing transfer to 



Solution C. (Bain rednctenr et reinfor^atenr} 



Gallic acid . . . . . . 5 gr. 



Tannin . . . . . . 3 gr. 



Fused potassium acetate . . . 10 gr. 



Distilled water . . . . . . 350 c.c. 



Keep in this for a few seconds. Then treat again with Solution B 

 till the preparation begins to turn black. Wash, dry, and mount. 



It is better, as Mervyn Gordon recommends, to leave the specimen 

 in B for two minutes and then to transfer to C for one and a half to two 

 minutes, and not to transfer again to B. It will also be found an 

 advantage to use a fresh supply of C for each preparation, a small 



