BACTERIAL FLAGELLA 75 



guinea pig were about 40 /x long and about 0*2 /li thick. The 

 single internal fibril extended only a short distance (about 4 /x) 

 up the shaft of the structure, and also penetrated about 1 (jl into 

 the cytoplasm of the cell. These structures lack most of the 

 characteristics of cilia, and in particular the basal body structure 

 from which all true cilia originate, so that the name stereocilia 

 should be abandoned for something more suitable. 



The structures found in the rat oviduct by Nilsson were 3 to 

 5 fJL long and 500 to 600 A in diameter, with double outer mem- 

 branes continuous with the cell membrane, and osmiophilic 

 material internally, either in the form of a ring, or in the form of 

 up to 6 fibrils. Occasionally these structures branch but the 

 arrangement of fibrils at the branch was not seen, nor was any 

 specialized structure seen in the basal cytoplasm. 



8. Bacterial Flagella 



Comparisons have sometimes been made between bacterial 

 flagella and the flagella borne by animals and plants ; these might 

 be expected to share many features since both appear to be 

 similar motile structures. Closer investigation reveals a number 

 of important diflFerences. Any attempts at comparison are com- 

 plicated by the fact that all bacterial flagella are evidently not the 

 same, and by the lack of detailed information about the structure 

 of bacterial flagella. In addition, Pijper (1957) has reviewed the 

 evidence for flagellar motility in bacteria and found it insufficient 

 for proof that the flagella are self -motile organelles, in spite of the 

 finding of Fleming, Voureka, Kramer and Hughes (1950) that 

 the flagella start to move before the bacteria do, and that flagella 

 may move on bacteria that are trapped and unable to move. 



De Robertis and Franchi (1951) studied the flagella oi Bacillus 

 hrevis under the electron microscope and found a central filament 

 some 120 to 150 A in diameter surrounded by a thin sheath. The 

 central strand appeared to be a double helix of a trypsin resistant 

 protein, with coiling of a variable pitch, while the sheath was 

 dissolved by trypsin. A triple-threaded helix has been described 

 by Starr and Williams (1952) in another motile bacillus. The 

 basal structure is also inconsistent, and, as Pijper points out, it is 

 not clear whether the flagella pass through the bacterial wall or not, 

 and therefore whether they are attached to any form of basal body. 



