8 GENERAL MORPHOLOGY AND BIOLOGY 



sometimes it goes on all through the life of the bacterium, 

 sometimes it ceases when sporulation is about to occur. Motility 

 is associated with the possession of fine wavy thread-like 

 appendages called flagella, which for their demonstration require 

 the application of special staining methods (vide Fig. 1, No. 12 ; 

 and Fig. 112). They have been shown to occur in many bacilli 

 and spirilla, but only in a few species of cocci. They vary in 

 length, but may be several times the length of the bacterium, 

 and may be at one or both extremities or all round. When 

 terminal they may occur singly or there may be several. The 

 nature of these flagella has been much disputed. Some have 

 held that, unlike what occurs in many alga?, they are not actual 

 prolongations of the bacterial protoplasm, but merely appendages 

 of the envelope, and have doubted whether they are really organs 

 of locomotion. There is now, however, little doubt that they 

 belong to the protoplasm. By appropriate means the central 

 parts of the latter can be made to shrink away from the peripheral 

 (vide infra, " plasmolysis "). In such a case movement goes on 

 as before, and in stained preparations the flagella can be seen 

 to be attached to the peripheral zone. It is to be noted that 

 flagella have never been demonstrated in non- motile bacteria, 

 while, on the other hand, they have been observed in nearly all 

 motile forms. There is little doubt, however, that all cases of 

 motility among the bacteria are not dependent on the possession 

 of flagella, for in some of the special spiral forms, and in most 

 of the higher bacteria, motility is probably due to contractility 

 of the protoplasm itself. 



The Minuter Structure of the Bacterial Protoplasm. Many attempts 

 have been made to obtain deeper information as to the structure of the 

 bacterial cell, and especially as to its behaviour in division. These 

 have largely turned on the interpretation to be put on certain appear- 

 ances which have been observed. These appearances are of two kinds. 

 First, under certain circumstances irregular deeply-stained granules are 

 observed in the protoplasm, often, when they occur in a bacillus, giving 

 the latter the appearance of a short chain of cocci. They are often 

 called metachromatic granules (vide Fig. 1, No. 16) from the fact that 

 by appropriate procedure they can be stained with one dye, and the 

 protoplasm in which they lie with another ; sometimes, when a single 

 stain is used, such as methylene blue, they assume a slightly different 

 tint from the protoplasm. 



For the demonstration of the metachromatic granules two methods 

 have been advanced. Ernst recommends that a few drops of Loffler's 

 methylene blue (vide p. 98) be placed on a cover-glass preparation and 

 the latter passed backwards and forwards over a Bunsen flame for half 

 a minute after steam begins to rise. The preparation is then washed 

 in water and counter-stained for one to two minutes in watery Bismarck- 

 brown. The granules are here stained blue, the protoplasm brown. 



