i22 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
The emulsion is made in the ordinary way, or for simply determining whether 
or no a bacterium has flagella I smear a mass of culture, moistened with water, over 
the slide in the same way as I would make a blood smear with a needle. So far I 
have used Van Ermengem's mordant osmic acid and tannin ; I have, however, got 
positive results bv using tannin alone after mordanting for some days, but have 
not made many experiments in this direction. 1 use then the following solutions : — 
r. Van Ermengem's mordant of osmic acid and tannin, one-half to one hour 
2. A o"i per cent, solution of silver nitrate 
3. 5 per cent, tannic acid + 5 per cent. NH, solution (partes aequales) 
Wash off the mordant thoroughly with tap-water. 
Pour some of the silver solution with a pipette over the slide, then add a 
few drops of the ammonium tannate solution till a deep reddish-brown colour is 
produced, and allow to stain for a minute or so, or as long as no black precipitate is 
formed. 
Wash off in ordinary tap-water. 
Repeat this procedure two or three times until the film has a deep brown or 
somewhat black colour. 
It is usual in describing a new method for staining flagella to claim that the 
preparations are most beautiful and quite free from precipitate, without asserting this, 
1 will simply say, that in my hands this method has given, with great ease, good 
preparations. 
