The Electrical Reactions of certain Bacteria, etc. 315 



It was a matter of considerable difficulty to keep a particular bacillus 

 continuously in view and thus watch its migration ; to obviate this, and in 

 view of the possibility of the observed movement being due to some variation 

 of surface tension of the fluid under the influence of the current, the experi- 

 mental arrangements were altered and observations made in the following 

 way : — ■ 



An emulsion of the Bacillus coli was made by pouring normal saline upon 

 a fresh agar culture of the organism, sweeping the growth by a platinum loop 

 into the saline, and pouring it into a test-tube, which was then sealed in the 

 blow-pipe ; by thorough agitation an even emulsion was made ; some of this 

 emulsion was then poured into a glass U-tube, fitted with platinum terminals 

 which just dipped beneath the liquid ; a current from Leclanche" cells was 

 sent through the emulsion. Observations at frecpient intervals showed that 

 the bacilli were accumulating under the anode in one limb of the U-tube ; 

 after several hours a dense column had formed, the fluid in the opposite limb 

 becoming clear ; reversing the current reversed the direction of motion of 

 the bacteria. 



A systematic series of tests was next undertaken with different bacteria 

 in various electrolytes. To expedite the work, four similar U -tubes were 

 mounted on a stand as seen in fig. 2, and observations made simultaneously 

 of the behaviour of the bacteria when suspended in different electrolytes, the 

 same current traversing the four solutions in series. The current was 



measured by a tangent galvanometer in circuit, and the voltage between the 

 terminals of the U -tubes by a voltmeter when required. Usually 4-per-cent. 

 solutions of the electrolytes were used ; with weaker solutions, e.g., ^ per cent., 

 gravitation of the bacteria to the bottom of the U -tubes occurred before the 

 electrical effect was evident. 



