CHAPTER III. 



POWER OF INDEPENDENT MOVEMENT IN BACTERIA. 



38. Molecular Movement and Locomotion. 



LIKE his predecessors, Chr. Ehrenberg considered the bacteria as animalcules, 

 and that, chiefly, because in not a few of them he discerned active locomotive 

 powers. For the same reason Pasteur was inclined in 1861 to regard his 

 " vibrion butyrique" as an infusorial animalcule. In opposition to this was 

 established the fact that the faculty of voluntary movement is not peculiar to 

 the bacteria, but is also possessed by many motile spores belonging to the algae ; 

 that is to say, by organisms unanimously admitted to be of vegetable nature. 



This motile power will now be more closely considered, both as regards its 

 nature and causes. 



The movement known as the Brownian or molecular movement which can 

 frequently be observed in small particles held in suspension in liquids, whereby 

 each particle describes a small orbit (sometimes rectilinear, sometimes circular or 

 oval) outside its horizontal axis of rotation is not included in this consideration. 

 The cause of this Brownian movement has not yet been examined with sufficient 

 accuracy ; but it is a purely physical one and in no wise physiological, since it is 

 manifested not only by living cocci, but also, as already stated, by emulsions of 

 many inanimate substances both of inorganic and organic nature. Ali-Cohen, 

 in his treatise referred to below, describes a very useful means by which one can 

 decide in doubtful cases whether the movement is independent or merely mole- 

 cular. According to the researches of Exner, the latter diminishes in briskness 

 as the viscosity of the circumambient liquid increases. If then a little of the 

 doubtful sample be mixed with a lukewarm liquefied 5 per cent, solution of 

 gelatin, both locomotive and molecular movement will at the outset remain un- 

 affected, but in proportion as the surrounding medium cools and becomes more 

 viscous, the latter movement will diminish, and finally cease altogether, whilst 

 the voluntary and independent movement will continue. 



By long-continued practice and observation the faculty will be gradually 

 acquired of distinguishing, without such aid, the so-called molecular from the 

 true voluntary bacterial movement, which we will now describe. This movement 

 is of two kinds, the first of which is occasioned by alternate contraction and 

 re-expansion of the plasma canal. This kind of movement qccurs in the case of 

 such thread bacteria as attach themselves to a support by one of their poles, and 

 then swing with a pendulous motion from this point of suspension, either 

 remaining in the same plane the while or describing a cone. 



39.-The Flag-ella or Cilia. 



Much more frequent is the second or roving movement, noticeable in free 

 unattached bacteria, and produced by special locomotive organs termed flagella 

 or cilia. These were first noticed by EHRENBERG (I.), in 1836, in a spirillum which 

 he discovered in a brook near Jena, and named Ophidomonas jeneusis. Closer 

 attention was first bestowed on these organs by COHN (I.). 



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