300 A MANUAL OF BACTERIOLOGY 



natural waters, there can be no serious doubt that 

 they will be equally successful in removing harmful 

 forms, which are not specially adapted for life in 

 water. Could it be, for instance, reasonably con- 

 tested that a method of purification which is capable 

 of removing the Bacillus aquatilis from water would 

 be incapable of disposing of the Bacillus anthracis, 

 when suspended in the same medium ? The sup- 

 position is, on the face of it, absurd, and not a par- 

 ticle of experimental evidence can be adduced in its 

 favour. It is, therefore, only rational to conclude 

 that those methods of water purification, both natural 

 and artificial, which succeed in most reducing the 

 total number of microbes, will also succeed in most 

 reducing the number of harmful forms should they 

 be present ' (Frankland). 



There are three methods by which microbes may 

 be absolutely removed from water. These are by 

 the agency of (a) electricity ; (b) heat ; (c) filtration 

 through porous porcelain. 



(a) Electricity. The author 1 has shown that the 

 electric current is capable of destroying the vitality 

 of several microbes when growing in liquid media. 

 For instance 



An E.M.F. of 2*16 volts destroys Bacillus tuberculosis, 

 ,, ,, 2 '26 ,, Bacterium lactis, 



,, ,, 3 '24 ,, Bacterium aceti, 



,, 3'3 ,, Bacterium allii, 



,, ,, 2'72 ,, Bacillus suUilis ; 



and an E.M.F. of 180 volts readily destroys the 



i Proceedings of Royal Society of Edinburgh, vol. xv. p. 45 ; 

 vol. xvii. p. 264 ; and Researches on Micro -Organisms, p. 177. 



