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 protoplasm 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 is used and a slide with a con- 

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

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

 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 

 T V oil immersion objective. If the preparation is kept warm for 

 some time, various vital phenomena may be noted. Direct division, 

 sporulation, motility, agglutination, and bacteriolysis 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 so 



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