94 APPLIED BACTERIOLOGY 



The cover-glasses, prepared and fixed as already directed 

 for Loffler's method, are covered with the osmic acid solu- 

 tion, which is allowed to act for half an hour. The cover- 

 glass is washed in a large excess of distilled water, and then 

 in alcohol. It is now dipped for three to five seconds in the 

 nitrate of silver solution (b), and then, without washing, 

 passed quickly through the gallo-tannic acid solution (c). 



The preparation is now washed again in a fresh quantity 

 of the silver nitrate solution (b), moving the cover-glass 

 about gently, and withdrawing it when the solution begins 

 to turn black. It is then washed thoroughly in several 

 changes of water, and mounted first in water and examined 

 with the yV inch oil immersion lens. If the preparation be 

 satisfactory, float off the slide, carefully air-dry, and mount 

 in xylol balsam. 



If the flagella are not sufficiently stained, the cover-glass 

 is again passed quickly through the gallo-tannin solution, 

 and then treated with the silver nitrate solution as directed 

 above. Care must be taken to change the nitrate of silver 

 solution as soon as any precipitation shows itself. 



Pitfielcl's Method. — Dr. Pitfield, of Philadelphia, has pub- 

 lished* the following process for the staining of flagella, 

 which consists of the use of but a single solution which is at 

 once mordant and stain : 



The solution should be made in two parts, which are 

 filtered and mixed — (a) saturated solution of alum, 10 c.c, 

 and saturated alcoholic solution of gentian violet, 1 c.c. ; 

 and (b) tannic acid, 1 gramme, and distilled water, 10 c.c. 

 The solutions should be made with cold water, and imme- 

 diately after mixing the stain is ready for use. The cover- 

 slip is to be carefully cleaned, the grease being burned off 

 in a flame, and after it has cooled the bacteria are spread 

 upon it, well diluted with water, care being taken to exclude 

 * Medical Neius, Philadelpliia, No. 10, vol. Ixvii. 



