76 LABORATORY GUIDE IN BACTERIOLOGY 



particles of carmin have a lively vibrating motion. 

 This is called "molecular movement," "Brownian 

 movement," or "pedesis." The particles scarcely 

 change their relative position. Actively motile or- 

 ganisms, on the contrary, change their relative posi- 

 tions. The movement of these may be slow, snake- 

 like, or like a fish swimming; or they may dart rapidly 

 across the field. 



Now observe and describe what changes have taken 

 place in the tube of broth with the hair. Compare 

 with a sterile tube, noting the turbidity, sediment, odor, 

 etc. Also examine in hanging drop. 



Examine the tube of glucose agar containing the 

 nail scrapings. Describe the general appearance, and 

 note whether gas bubbles are present. 



EXERCISE 6 



Make stained preparations of three different 

 colonies, using the three stains: i.e., gentian violet, 

 methylene blue, and carbol fuchsin, also a Gram stain. 



Method of making stained preparations — 



1. Clean and flame a cover slip, or, if preferred, a 

 slide may be used for this purpose. Cover shps, if 

 handled by the fingers, should be held by the edges. 

 Use as much as possible the forceps made for that pur- 

 pose. After handUng, the forceps should be sterilized 

 in the flame. 



2. Place one loopful of water on the cover slip. 



3. Take a small quantity of the colony or culture 

 on a platinum needle and mix with water until faintly 

 cloudy. Burn the remainder of the culture off the 

 needle. 



