24 BACTERIOLOGICAL EXAMINATION OF WATER. 



statement that there is no direct and constant relation between 

 the chemical composition and the number of micro-organisms ; 

 but, speaking generally, it may be said that those waters which 

 contain much organic matter usually show a high bacterial 

 count. 



THE ACTION OF ELECTRICITY ON BACTERIA. 



The action of electricity on bacteria was first investigated by 

 Schiel, who judged the action of the electric current by an 

 examination of its effects on the motility of micro-organisms. 

 Colin and Benno Mendelsohn used a purely mineral solution 

 containing 5 grammes of potassium phosphate, 5 grammes of 

 sulphate of magnesia, 10 grammes of neutral tartrate of 

 ammonia, and 0'5 gramme of calcium chloride per litre. The 

 nutritive fluid was placed in a U-tube, then inoculated with the 

 micro-organism to be studied, and a current from several 

 elements of Marie-Davy pile passed through it. If a growth 

 occurred the current was deemed to have had no action. If no 

 growth took place this might have been due to the death of the 

 bacteria or to changes having taken place in the fluid which 

 rendered it an unfavourable medium. To judge these effects a 

 loopful was withdrawn from the U-tube and planted out on some 

 fresh medium, and a new culture was then inoculated into the 

 tube. Cohn and Mendelsohn found that when the action of the 

 current was short and feeble its effect on bacteria was nil. 

 When the current from two powerful elements acted for twenty- 

 four hours the bacteria were not killed, but the fluid was so 

 altered that bacteria would not grow in it. When the current 

 from five elements acted for twenty-four hours the bacteria 

 were killed at both poles, and the fluid was rendered sterile and 

 profoundly modified. In order to prevent the decomposition of 

 the fluid by the current, induction currents were tried but 

 without any appreciable result. Experiments were then made 

 by passing an electric current through a potato sown with 

 B. prodigiosus. Chemical effects were also produced in the 

 potato, just as in the nutritive fluid, so that though the bacillus 

 was killed, its death could not be ascribed to the physical action 

 of the current. Prochownick and Spaeth covered the plates of 

 the battery with nutritive agar, which were then infected with 



