INFLUENCE OF MECHANICAL SHOCK 65 



particularly demonstrated in the case of B. ruber. Meltzer therefore arrived 

 at the following conclusions : Slight concussion favours tho 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 become 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 

 nutrient gelatin arranged themselves in the form of a feather, and in such a 

 manner that the individual rays grew in a slanting upward direction. When 

 the tubes containing the cultures were placed radially on a rapidly-revolving 

 horizontal glass disc, the vegetation then developing assumed an appearance 

 corresponding to that already described, the individual rays, which extended 

 from the axis of the puncture, formed acute angles therewith, the apertures of 

 which were reflected towards the centre of the disc. This species therefore 

 exhibits negative geotropism. BEYERINCK (III-) erroneously, as the author 

 conceives has denied this fact. 



The lower fungi generally, and bacteria in particular, remain, within wide 

 limits, unaffected by high gaseous pressure. Thus, SCHAFFER and FREUDENREICH 

 (I.) and others have inoculated samples of milk with different bacteria (those of 

 anthrax and typhus among them), and then exposed them for seven days to 

 carbon dioxide at a pressure of fifty atmospheres, without being able to cause 

 any appreciable injury to the organisms. Similar behaviour was also observed 

 with oxygen under a pressure of twenty- one atmospheres, prolonged for a week. 

 There is, therefore, no reason for hoping that liquids which are injuriously 

 affected by heat can be sterilised in the cold by the aid of gas (C0 2 , O, air) 

 under high pressure. For exhaustive experiments on the influence of high 

 gaseous pressure on living creatures generally, and the pathogenic Schizomycetes 

 in particular, we are indebted to Paul Bert. 



