24 



With the loop, remove a drop of the liquid culture and 

 place it on the middle of the cover-glass. With a pair of 

 fine forceps invert the cover-glass over the glass ring fixed 

 to a slide for this purpose. The surface of the ring should 

 previously be moistened with liquid vaseline to prevent the 

 cover-glass from sliding. The preparation is then ready for 

 examination. Examine it first with the high power dry lens 

 and then with the oil immersion objective. (For directions 

 in the use of the microscope see " The Microscope" by Pro- 

 fessor S. H. Gage.) (2) From cultures on solid media. On 

 account of the very large number of bacteria in the growth 

 on solid media it is necessary to separate them in a clear 

 liquid. Take a cover-glass as before and place a loopful of 

 sterilized water or bouillon on the center. With the plati- 

 num needle touch the surface growth very gently with the 

 end of the needle and carefully rinse it in the drop of liquid 

 on the cover-glass. From this point the examination is the 

 same as with the liquid culture. Upon examination, if the 

 bacteria are so numerous that the individual organisms can 

 not be clearly distinguished, i.e., separated from each other, 

 the preparation must be rejected and another one made, 

 using a smaller quantity of the growth. 



§ 26. Suggestions for the microscopic examination of 

 bacteria. In examining the bacteria, as they appear under 

 the microscope in the hanging drop preparations, the follow- 

 ing features should be observed : Are the individual bacteria 

 spherical, rod-shaped or spiral in form ? Are they .single or 

 united in pairs, masses or clumps, or in shorter or longer 

 chains ? For this determination it is better to examine the 

 edge of the drop. Are they motile, that is, do the individual 

 bacteria move from one point in the field to another ? To 

 determine this the center of the drop is better. Clearly dis- 

 tinguish between motility and a simple dancing motion. 

 Determine the presence or absence of spores. These are 

 bright highly refractory bodies either within or outside of 



