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 LAQUERRIERE (I.), PRO- 

 CHOWNIK and SPATH (I.), and DUCLAUX (III.). The same method 

 of experimenting was followed by all these observers, and con- 

 sisted in passing an electric current through the culture. Cohn 

 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 rendered 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 

 therefore 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 experi- 

 ment a current of 0.5 to i.o ampere reduced the number of 

 germs to between -\jth and xJ^th of the initial quantity. 



To ascertain 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 



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