STAINING 195 



is apt to cause the film on the surface of the mordant to 

 settle down on the slide and spoil the preparation. After 

 the mordant is washed off and all traces of it removed with 

 a clean cloth if necessary the stain is applied and gently 

 heated and cooled the same way for from three to five min- 

 utes. The preparation is then washed, dried and examined. 



The mordant used is a modification of LofHer's which is 

 somewhat simpler in preparation since the stock solution of 

 FeCls is more permanent than FeS04 solution. 



Mordant sufficient for one student: 



5 per cent, solution of FeCls 20.0 c.c. 



25 per cent', solution of tannic acid . . 20.0 c.c. 



Anilin fuchsin . . . 4.0 c.c. 



Normal NaOH .. 1.5 c.c. 



The solution of FeCls is made up in the cold and must be 

 perfectly clear. The tannic acid solution must be thor- 

 oughly boiled and filtered until clear. The iron and the acid 

 are carefully mixed, boiled and filtered clear. The anilin 

 fuchsin must be added slowly with constant stirring and the 

 mixture boiled and filtered. The NaOH is added in the 

 same way. The final mordant should not leave a film on a 

 clean slide when poured on and allowed to run ofl'. Unless 

 the mordant is in this condition and perfectly clear, it should 

 not be used, but a new one must be made up. Time and 

 care in the preparation of the mordant are essential. 



The stain to follow this mordant is anilin fuchsin. 



By the use of the hanging drop slide and the methods of 

 staining just described all the various morphological fea- 

 tures of the bacterial cell may be ascertained. 



It is necessary when cell gmipings as characteristic of 

 definite modes of division are to be determined to make slides 

 from a liquid culture, as broth. Place a drop of the material, 

 preferably from the bottom of the tube in most instances, 

 from the top in case a pellicle or scum is formed on the sur- 

 face, on the slide and allow this to dry without spreading it 

 out, then stain lightly with Lofiler's blue. Such slides also 

 show characteristic cell forms as well. Slides should be 

 made from solid media to show variations in form and size 

 and involution forms. These latter are especially apt to 

 occur on potato media, 



