INFLUENCE OF MECHANICAL SHOCK. 83 



The restriction of reproduction thus indicated increased with the 

 duration of the treatment, so that by this means the liquid could be 

 completely freed from germs. The effect was even more powerful 

 when sterilised glass beads were added before commencing the 

 operation, the complete annihilation of the germs being accom- 

 plished under these conditions by ten hours' agitation. In addi- 

 tion to B. megatherium, Meltzer also included a micrococcus (pre- 

 sumbly M. radiatus, Flugge) and a short motile bacillus (albus ?) 

 in the scope of his investigations. A difference in the degree of 

 resistance to this kind of inhibition is inherent in these organisms, 

 since it was found possible to successively eliminate each form 

 from a mixture of the three species. E. megatherium, as the most 

 susceptible, disappeared first, and was followed, in order, by Micro- 

 coccus radiatus and Bacillus albus. The cells were, as a result 

 of the shaking, split up, not into visible debris, but into an in- 

 distinguishable fine powder, a circumstance showing that the 

 destruction of the vitality of the cell was not the result of a coarse 

 mechanical disruption, but was due to a much more refined pro- 

 cess ; as was, in fact, shown by the further researches made by the 

 same observer. He left several flasks containing cultures of B. 

 megatherium or B. subtilis in solutions of common salt, to stand 

 for several days in the engine-house of a large New York brewery, 

 wherein, in consequence of the uninterrupted working of the 

 engine, an incessant vibration was produced throughout the room. 

 After four days all the germs in the several flasks were dead, 

 whilst energetic reproduction had proceeded in the check samples 

 placed in a quiet spot. Consequently, not only violent shocks, 

 but also minute vibrations, exhibit the power of retarding the 

 growth of bacteria, and even killing the organism. 



Motion may, however, also exert a favourable influence, and 

 especially when it is comparatively weak, reproduction being 

 thereby accelerated, as has been more particularly demonstrated in 

 the case of B. ruber. Meltzer therefore arrived at the following 

 conclusions : Slight concussion favours the vitality of micro- 

 organisms and has a stimulative effect, the rate of reproduction 

 being highest when the optimum of vibration is obtained ; but 

 from this point onwards the restrictive effects of concussion be- 

 come manifest. The constants of optimum and maximum effect 

 have different values for different organisms. That degree of 

 concussion which is injurious for one species may be favourable to 

 a second, and without any appreciable effect on a third. This 

 explains the contradictory reports made by the pioneers in this 

 field, each of whom experimented on different organisms. 



The influence of gravity on the direction of growth, which 

 comes into play in the higher plants, and the effects of which 

 are known in Vegetable Physiology as geotropism, has also 

 been observed in the Schizomycetes. BOYCE and EVANS (I.) found 

 that vertically disposed puncture-cultures of Bacterium Zopfii in 



