MOTILITY 



53 



ficial media often lose their Gram-staining characteristics; hence it is 

 desirable to determine this staining reaction in cultures freshly isolated. 

 Be sure that the stains, especially the aniline gentian violet and the 

 iodine solution, have not deteriorated. There is no more important 

 stain than this, and none which requires greater experience. The chief 

 causes of conflicting results are i. working with old cultures and 2. not. 

 having satisfactory staining solutions. 



FIG. ii. Series of stab cultures in gelatin, showing modes of growth of different 

 species of bacteria. (Abbott.') 



Motility, as stated above, is at times difficult to determine. For this purpose 

 young eighteen-hour-old bouillon cultures are preferable, and the preparation should 

 be made by applying a vaseline ring to the slide, then putting a drop of the bouillon 

 culture in the center of the ring (or a drop of water inoculated from an agar slant 

 growth), then putting on a cover-glass. By this method current movement is done 

 away with and the preparation keeps for hours. This is a convenient method for 

 agglutination tests. The hanging drop with a concave slide is ordinarily used. 

 With this, cut down the light and focus on the margin of the drop with the %- 

 inch objective before examining with a high dry objective (% inch). 



