6 BACTERIOLOGY 



to thick sturdy filaments. They are of uniform thickness, or 

 may show slight nodular swellings, as in E-F, Fig. 2. They 

 may be continuous or branched. It is to the lashing movement 

 of these organs that the bacterium owes its motility. In the 

 genus Bacterium of Migula flagella are absent, and the organ- 

 isms show no progressive motility, but as a rule only a vibratory 

 motion, the Broivnian movement. In certain non-flagellated 

 forms a slow rotatory or squirming motion may result from suc- 

 cessive dilation and contraction of the membrane. The flagella 

 vary as to their arrangement ; and on this is based the classifica- 

 tion of the genera Bacillus and Pseudomonas. In Bacillus the 

 flagella are pcritricJiic ; that is, they may originate from any part 

 of the capsule, and frequently surround the organism, as in F, 

 Fig. 2. In Pseudomonas the flagella are polar or bipolar; that 

 is, a" single flagellum may arise from one or both poles of the rod, 

 as in E, Fig. 2. Fischer distinguishes two types of polar flagella, 

 i.e. moiiotricliic, where they occur singly as in Pseudomonas, 

 and lophotrichic, where they occur in tufts of two or more, as in 

 Spirillum. 



D. The Staining of Flagella 



This is a matter requiring the greatest skill, and but few 

 bacteriologists are uniformly successful. Certain precautions 

 are essential to good results. In the first place the cover-glasses 

 must be absolutely clean and free from every trace of grease. If 

 an oese of water be placed on a cover-glass it should spread 

 evenly over the entire surface, and remain so ; otherwise it is 

 not in a suitable condition. Four or five of these should be 

 placed in a row on a piece of black paper or tile, and on each an 

 oese-full of water should be deposited. A twenty-four hour 

 agar culture should be ready at hand. With a platinum wire, 

 remove a very small portion of the pure culture without touching 

 the underlying medium. With a single circular motion, no 

 more, since too much manipulation is apt to injure the delicate 

 flagella, mix the culture with the water on the first cover-glass, 



