io GENERAL MORPHOLOG Y AND BIOLOG Y. 



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 algre, 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 de- 

 pendent 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 informa- 

 tion 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 appearances 

 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 appear- 

 ance of a short chain of cocci. They are often called 

 metachromatic granules (vide Fig. i, 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. 



