MECHANICAL ACTIVITY. 55 



U MECHANICAL ACTIVITY. 



I Under the microscope we easily observe that many bac- 

 ria present pronounced inherent motion, and by study 

 it is found that almost all the motile varieties 1 possess 

 flagella by means of which they propel themselves. The 

 character of the motion is exceedingly variable; for ex- 

 ample, creeping (B. megatherium), wabbling (B. subtilis), 

 rolling, snake-like (vibriones) ; sometimes it is very slow, 

 and sometimes so rapid that any detailed observation can 

 scarcely be made (B. typhi). 



In many cases it is difficult to decide whether true 

 active motion is present, or whether the micro-organisms 

 present especially well-marked Brownian or molecular 

 motion — i. e., the dancing and tremor exhibited also by 

 finely divided inorganic particles. In such a case it is 

 recommended to try to render the flagella visible by stain- 

 ing (Technical Appendix), and also to examine the organ- 

 ism in a drop of 5% carbolic acid or 1 : 1000 sublimate 

 solution, when, if the motion still persists, we have only 

 to do with molecular motion. Many varieties appear on 

 brief observation to be quiet, but on longer examination 

 single individuals are observed to exhibit positive motion. 

 It seems that the endowments with flagella and motility, 

 when once present, are for the most part reasonably con- 

 stant peculiarities. Many varieties do not always present 

 motility, it being absent, especially, on many media. Ac- 

 cording to A. Fischer, with faultlessly developed flagella 

 motion may be absent ; for example, in Bac. subtilis on a 

 nutrient medium containing 2% to 4% of ammonium chlo- 

 rid. We have never observed spontaneous motion or fla- 

 gella in two different cultures of the Micrococcus agilis Ali- 

 Cohen, obtained from reliable sources and grown upon all 

 ordinary media. We have arrived at the conviction that 

 the same variety may occur either with or without flagella. 

 (Compare special part. ) 



Th. Smith has described a non-motile form of the mo- 



1 Upon the actively motile Spirochete Obermeieri and the slowly 

 creeping Beggiatoa no flagella have thus far been demonstrated ; there- 

 fore the motion is supposed to depend upon a narrow undulating 

 membrane attached to the organism. 



