and Laboratory Methods. 



2427 



of the drop with the low power and without moving 

 the slide, place the higher power, one-sixth inch, 

 in position. Open the diaphragm slightly and 

 focus without moving the slide, until the edge of 

 the drop appears as a sharp line. The bacteria 

 should be readily detected. If not it is probably 

 because the light is not right. Adjust this by 

 slightly opening or closing the diaphragm. 



Make " hanging drop " preparations from dif- 

 ferent colonies on the potato cultures. Also from 

 the hay infusion. 



Note the ability of certain forms to move from place to place. Many of them 

 will exhibit characteristic "gaits." This power of independent movement is due 

 to certain hair like appendages known as fJagel/a which are distributed in various 

 ways on the different forms. Some of the more common modes of distribution 



Fig. 1.5. — Slide arranged for mak- 

 ing a hanging drop preparation. 

 1, glass slide; 2, block of blot- 

 ting or filter paper ; ."!, cover- 

 glass ; 4, drop of water contain- 

 ing bacteria to be examined. 



Fig. 16. — Diagram illustrating flagellated bacteria. 



are shown in Fig. 16. These flagella are only visible when they are stained, 

 and the method of staining is one of the most difficult of bacteriological proce- 

 dures. 



Forms which are incapable of progressive movement show a vibratory move- 

 ment known from the discoverer as the Brownian movement, a property common 

 to all finely divided matter in suspension. 



3. ^. 5. 



Fig. 17. — Diagram illustrating spore formation among bacteria. 



