STAINING OP PLAGELLA 93 



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 xV iiich 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. 



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

 blished* 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 (&) 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 

 culture medium. After the preparation has been thoroughly 

 dried in the air, it should be held over the flame with the 

 fingers, as Loffler has directed. Afterwards the stain is 

 gradually poured on the slip and heated gently, the fluid 

 being brought almost to boiling-point; the slip, covered 

 with the hot stain, should then be laid aside for one minute, 

 washed in water, and mounted. Upon examination, the 

 bacteria, both isolated and in clumps, will, if motile, be 

 found to have the flagella clearly and delicately defined. 

 * Medical News, Philadelphia, No. 10, vo], Ixvii. 



