CHAPTER III. 



POWER OF INDEPENDENT MOVEMENT IN BACTERIA. 



38. Molecular Movement and Locomotion. 



LIKE his predecessors, Chr. Ehrenberg considered the bacteria as 

 animalculse, 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 move- 

 ment 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 considera- 

 tion. 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 molecular. 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 unaffected, 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, 



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