60 GENERAL CONDITIONS FOR GROWTH 



been shown by several experimenters and also by finding 

 living bacteria in the ooze dredged from the bottom of the 

 ocean at depths of several miles. 



Pressures from 10,000 to 100,000 pounds show variable 

 effects. Some bacteria are readily killed and others, even 

 non-spore formers, are only slightly affected. The time 

 factor is important in this connection. The presence of 

 acids, even CO2, or organic acids, results in the destruction 

 of most non-spore formers. 



MECHANICAL VIBRATION. 



Vibrations transmitted to bacteria in a liquid may be 

 injurious to them under certain circumstances. Some of 

 the larger forms, like Bacillus suhtilis, may be completely 

 destroyed by shaking in a rapidly moving shaking machine 

 in a few hours. Bacteria in liquids placed on portions of 

 machinery where only a slight trembling is felt have been 

 found to be killed after several days. Reinke has shown 

 that the passing of strong sound waves through bacterial 

 growths markedly inhibits their development. 



HIGH FREQUENCY VIBRATIONS. 



The injurious effects of high frequency sound waves, up to 

 millions per second, produced by quartz crystals under the 

 influence of electric forces have been studied on mice and other 

 small animals and their heating effect on man has been noted. 

 Also some experiments on high frequency electric currents, 

 66,000,000 to 68,000,000 per second, on certain tumor (sarcoma) 

 cells in mice have been reported;^ The author has been expect- 

 ing to read of similar work on bacteria. If it has appeared 

 it has escaped his notice. One would anticipate markedly 

 injurious action from either of the above "high frequency 

 vibrations." Whether they would have practical use against 

 bacteria requires further study. 



1 Schereschewsky, J. W. and Andervont, H. B. : "The Action of Cur- 

 rents of Very High Frequency upon Tissue Cells," Public Health Reports, 

 April 20, 1928, pp. 927-945. 



