40 METHODS OF STUDYING MICROORGANISMS 



or 20 C. After these tubes and plates have been " incubated" 

 for twenty-four to forty- eight hours the bacteriologist 

 observes them and takes note of the evidences of growth. 

 He will make stained preparations for microscopic observa- 

 tion and note the morphology of the plant. Many stains are 

 in use for demonstrating various characteristics. He will 

 also prepare what is known as a "hanging drop." This 



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FIG. 12. Platinum needle and loop. (Park.) 



consists of a drop of fluid broth culture upon a thin cover 

 inverted over a depression ground into a glass slide (Fig. 14). 

 He will discover from this preparation under the microscope 

 the presence of motility and the manner of division of the 

 bacteria. From his tube cultures he chiefly finds out whether 

 the bacteria develop enzymes. To solid media (agar-agar) 

 he may add various sugars to discover the fermentative 

 powers of the bacterium. The fermentative powers may also 



