6 INTRODUCTION 



or incubator for four days. Transfer the drop on the wire loop 

 to a clean slide : put on cover-glass and examine with low power, 

 and then with -J -inch objective. Make drawings of bacteria seen. 

 Before and after using a platinum loop or needle always heat 

 it to redness in Bunsen flame : when not in use keep it on a 

 stand (Fig. 3) ; do not place it on the laboratory table or bench. 

 Ex. 3. Make infusions of the leaves of cabbage, cereals, 

 clover, and other plants. Pour off the liquid, after it has 

 been on the leaves for three or four hours, into a clean beaker. 

 Leave in a warm room for four days, and examine drops as in 

 preceding exercise. Make drawings of bacteria seen. 



Ex. 4. Take some peas and soak them in water all night. 

 Then boil them for five minutes, and leave them to stand in the 



boiled water for a day 

 or two in a warm room. 

 Take a drop of the 

 liquid and examine for 



FIG. 3. Copper stand for platinum needles bacteria. 



and loops. 



Ex. 5. Staining of 



Bacteria. Since bacteria are transparent and not readily seen, 

 they are frequently killed and stained, when their form is 

 rendered more easily visible. 



(1) Prepare a saturated solution of gentian violet in alcohol, 

 using 



Gentian violet . . . . . . 4 gr. 



Absolute alcohol . ' . . . . 50 c.c. 

 Shake well, and allow it to stand twenty-four hours ; then filter 

 twice into a stoppered bottle ; label it, and keep for future use. 



(2) Add three drops of the above alcoholic solution to a 

 watch-glass containing distilled water. 



(3) Take single drops of the infusions from Exs. 3 and 4 and 

 spread them with the platinum loop as thin films over the surface 

 of clean cover-glasses. Cover with a beaker to keep off dust, 

 and allow the films to dry. The moisture evaporates and leaves 

 the bacteria behind on the glasses. 



