CHAPTER V 

 STUDY OF BACTERIA 



Bacteria are studied in the following various ways: 



1. Morphological characteristics, form, size, motility, presence 

 of spores, granules, capsules, and flagella. Reaction of proto- 

 plasm to dyes and reagents. 



2. Characteristics of growth in culture media; appearances of 

 culture; chemical activities; production of acid, gases, toxins, 

 colors, etc.; reactions to heat, disinfectants, light, etc. 



3. Study of the action of bacteria on the tissues of man and 

 animals, and of the toxins on the tissues and functions of the 

 various organisms. 



The simplest way to study bacteria is to make a hanging drop of 

 a fluid containing bacteria, and observing the organisms under a 

 microscope. To do this, a cover-slip, and a slide with a concavity 

 ground in it are used. A drop of bacteria laden fluid is placed on 

 the cover-glass, and after the edges have been smeared with vase- 

 line, the cover-slip is inverted over the concavity in the slide, and 

 the bacteria can then be examined with either the dry % inch, or 

 the one-twelfth oil immersion objective. If the preparation is 

 kept warm for some time, various vital phenomena may be noted. 

 Direct division, sporulation, motility, agglutination, and bacterio- 

 lysis can be studied by this means. Instead of using a fluid, a 

 block of nutrient agar may be cemented to the cover-glass; after 

 the bacteria have been planted on the agar, the various vital 

 phenomena may be noted. 



All minute bodies, whether they be bacteria, dust particles or 

 granules of india ink in suspension, exhibit a trembling vibrating 

 motion called the Brownian motion. Motile bacteria either move 



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