MOTILITY. 9 



devised for the purpose (vide p. 114) ; (2) the fact that the 

 bacterium containing the spore has higher powers of re- 

 sistance against inimical conditions than a vegetative form. 

 It is important to bear these tests in mind, as in some 

 of the smaller bacteria especially, it is very difficult to 

 say whether they spore or not. There may appear in such 

 organisms small unstained spots the significance of which 

 it is very difficult to determine. 



The Question of Arthrosporous Bacteria. It is stated by Hueppe 

 that among certain organisms, e.g.> some streptococci, certain indi- 

 viduals may without endogenous sporulation take on a resting stage. 

 These become s\vollen, stain well with ordinary stains, and they are 

 stated to have higher power of resistance than the other forms ; further, 

 when vegetative life again occurs it is from them that multiplication 

 is said to take place. From the fact that there is no new formation 

 within the protoplasm, but that it is the whole of the latter which 

 participates, in the change, these individuals have been called arthro- 

 spores. The existence of such special individuals amongst the lower 

 bacteria is extremely problematical. They have no distinct capsule, 

 and they present no special staining reactions, nor any microscopic 

 features by which they can be certainly recognised, while their alleged 

 increased powers of resistance are very doubtful. All the phenomena 

 noted can be explained by the undoubted fact that in an ordinary 

 growth there is very great variation among the individual organisms 

 in their powers of resistance to external conditions. 



Motility. As has been stated, many bacteria are motile. 

 Motility can be studied by means of hanging drop prepara- 

 tions (vide p. 74). The movements are of a darting, roll- 

 ing or vibratile character. The degree of motility depends 

 on the temperature, on the age of the growth, and on the 

 medium in which the bacteria are. Sometimes the move- 

 ments are most active just after the cell has multiplied, 

 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. i, No. 12 ; and Fig. 86). 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 



