CHAPTER IL. 
STAINING TECHNIQUE 
SincE bacteria are such small organisms, they must be examined 
collectively and only in rare instances as individuals. Barber (1914) 
devised a method whereby single cells may be isolated, but this pro- 
cedure is better adapted to advanced work where very accurate results 
are desired. For ordinary work the bacteria may be grown either in 
liquid or solid media. From these media they may be put on slides 
according to instructions which are given later. After these slides 
or cover glasses have been examined they should be dropped into a 
disinfectant since Rettger (1913) has pointed out that the staining 
procedure may not kill the organism. 
Hanging Drop. This preparation enables the bacteriologist to 
observe bacteria under the microscope in the free condition and not 
fastened to the slide as in the staining methods. There are several 
adaptations of this method all of which lead to the same results, i.e., 
suspending the organisms in a drop of fluid in a well of some sort. 
Some of the more important of these are mentioned below. 
Koch’s Concave Slide. This consists of a plain glass slide with a 
hollow well ground in the middle. The cover glass with the culture 
is placed over this. Such a slide is quite satisfactory for the exam- 
ination of bacteria, but may be too shallow for the study and continued 
observation of molds since the mycelium will soon-fill the cell. For 
this purpose other slides of a similar nature will be found to give 
better results. 
Bottcher’s Moist Chamber. This is essentially for the same pur- 
pose as the concave slide, but is constructed in such a way that a deeper 
well is secured. ‘These may be made by fastening to an ordinary glass 
slide a glass or rubber ring about 16 mm. in diameter and 2 to 3 mm. 
high. These are inexpensive and may be easily glued to the slide. A 
preparation made with one of these may be securely sealed with vaseline 
and thereby prevent evaporation which is an important factor if con- 
tinued observations are.to be made. Other forms of apparatus which 
may be used in this relation are shown in Fig. 30. 
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