MECHANICAL AGITATION 61 



§5. MECHANICAL AGITATION. 



It was at one time thought that no living organism could continue 

 to exist unless it obtained a certain amount of repose for reproductive 

 purposes. It was, however, demonstrated that there were algae 

 living beneath large waterfalls, and consequently always subjected to 

 agitation, which were evidently able to exist and to carry on their 

 reproductive processes even whilst being violently agitated. However, 

 bacteria do suffer if violently agitated. Thus, it has been found that 

 when they were placed in a shaking machine which made a hundred 

 movements per minute, each with an amplitude of ten inches, for 

 48 hours, the agitation proved fatal to the bacteria. Conclusive 

 results were obtained by Meltzcr. He used the agitator of a New 

 York mineral water works, which subjected the samples to 180 

 reversed movements per minute, the amplitude of each movement 

 being 40 cms. This process decreased the number of germs, and, 

 when it was long continued, they disappeared altogether. When glass 

 beads were added to the sample, the experimenter found that the 

 process of extinction was expedited, ten hours being sufficient to kill 

 the whole number present. He also found that there is a difference in 

 the degree of resistance offered by bacteria, some holding out longer 

 than others. As a result of the shaking the bacteria were split up 

 into an extremely fine powder. The same observer found that when 

 cultures of Bac. subtilis or Bac. megatherium were placed for four days 

 in the engine room of a brewery, where, in consequence of the 

 working of the engine, the whole room was subjected to vibration, all 

 the bacteria in the cultures were destroyed. 



When not too violent, however, motion is favourable to the well- 

 being of bacteria and allied organisms. Thus, E. Chr. Hansen found 

 that yeast developed better when the beer-wort was set in motion by 

 stirrers. In the case of Bac. ruber it has been ascertained that the 

 power of reproduction is improved by slight movement. When, 

 starting from rest, the motion is gradually increased, an optimum is 

 reached, beyond which the motion impedes the power of reproduction 

 until finally a point is reached when the motility is such as to cause 

 destruction. As would be expected, the optimum varies for different 

 species, the hardier bacilli, for example, being able to stand a good 

 deal more shaking than the weaker spirilla. 



