SECTION II. 

 GENERAL BIOLOGY AND CLASSIFICATION OF BACTERIA. 



CHAPTER VII. 



THE BACTERIA UNDER THE INFLUENCE OF 

 PHYSICAL AGENCIES. 



60. Influence of Electricity. 



THE effects of this agency were first recorded by SCHIEL (I.) in 1875, the earliest 

 exhaustive researches being carried out by COHN and MENDELSOHN (I.) in 1879, 

 succeeded in following years by the labours of APOSTOLI and LAQUERRI^RE (I.), 

 PEOCHOWNIK and SPATH (I.), and DUCLAUX (III.)- The same method of experi- 

 menting was followed by all these observers, and consisted in passing an electric 

 current through the culture. Conn found that, to produce an appreciable 

 weakening effect by this means, a battery of at least two cells was required, the 

 current from which, when passed for 12-24 hours through a nutrient solution 

 inoculated with bacteria, was unable to kill the germs, but nevertheless ren- 

 dered the medium unsuitable for further culture. This result, as explained by 

 Cohn, was due to the action of the current in forming decomposition products 

 inimical to fungi. Bearing this in mind, such a method of experiment is there- 

 fore unsuitable for affording a clear insight into the influence of the current 

 itself. These labours are, nevertheless, worthy of mention, since, having been 

 further pursued with a practical aim, they have led to the elaboration of a 

 process for the purification of sewage water (as developed and tested by WEBSTER 

 (I.) in particular). The water to be purified is led through a trough into which 

 dip large iron plates, acting as electrodes for a powerful current generated by a 

 dynamo machine and passed through the liquid. FERMI (I.) tested the process 

 from a bacteriological point of view, and ascertained that under the conditions 

 of the experiment a current of 0.5 to i o ampere reduced the number of germs 

 to between ^th and y^th of the initial quantity. 



To as-certain the effect of the electric current, unaffected by secondary 

 chemical influences, BURCI and FRASCANI (I.) proceeded by drying the bacteria 

 (i.e. a small portion of inoculated nutrient solution) on a pad of glass wool at 

 37 0., and then dipping the pad into mercury through which a constant galvanic 

 current was being passed. In this case the bacteria were killed ; but the method 

 of experimenting is not free from objection, since the dried constituents of the 

 medium were present along with the bacteria, and might retain moisture and 

 form decomposition products noxious to the latter. 



These injurious secondary influences can only be perfectly excluded when 

 the electric current is prevented from coming into contact with the nutrient 

 medium, a condition first attained in the experimental method selected by 

 SPILKER (I.) and GOTTSTEIN (I.). The glass flask containing the bacterial culture 

 was enveloped by a coil of the line wire, and an induction current then passed. 



57 



