Dr Shearer, The action of electrolytes on the electrical, etc. 263 



The action of electrolytes on the electrical conductivity of the 

 bacterial cell and their effect on the rate of migration of these cells 

 in an electric field. By C. Shearer, Sc.D., F.R.S., Clare College. 

 (From the Pathological Laboratory, Cambridge.) 



{Read 17 February 1919.] 



If a thick creamy emulsion of the meningococcus or B. coli is 

 made up in neutral Ringer's solution (that is, one in which the 

 sodium bicarbonate is left out), and the conductivity measured by 

 means of a Kohlrausch bridge and cell; it is found that its resistance 

 is more than treble that of the same solution without the bacteria : 

 that is the greater part of the resistance is due to the presence of 

 the bacteria. 



This determination was made as follows: a 24 hour culture of 

 the meningococcus or B. coli on trypagar (2-t plates) was washed 

 off in a considerable quantity of Ringer's solution, centrifuged down 

 and re washed several times in a similar manner to remove all traces 

 of serum or any salts derived from the culture medium. The centri- 

 fuged deposit was then made up to standard strength in neutral 

 Ringer's solution, so that it was not too thick to be sucked up in a 

 medium sized pipette and transferred to a Hamburger cell and its 

 conductivity determined. It was found that the conductivity of 

 such standard emulsions when measured under similar conditions 

 of temperature was fairly uniform*. When sufficient care was 

 taken to get the emulsions of the right thickness, resistances of 

 110 ohms could be pretty constantly obtained. The same quantity 

 of Ringer's solution alone had about 26"7 ohms resistance under 

 the same conditions. 



If, however, in place of the Ringer's solution we make up the 

 bacterial emulsions in pure sodium chloride of the same conducti- 

 vity as that of the Ringer's solution, i.e. one in which the resistance 

 is 26'7 ohms (which corresponds to a NaCl solution of about 0'85 °/^), 

 we obtain as in the case of the emulsion in Ringer's solution an 

 initial resistance of 110 ohms. Within a few minutes, however, this 

 gradually drops and at the end of 30 or 40 minutes the emulsion 

 now has the same conductivity as that of the bare sodium chloride 

 solution without the bacteria, i.e. 26'7 ohms resistance. Thus pure 

 sodium chloride of about the concentration as that present in the 

 blood gradually destroys the resistance of the bacterial cell. If the 

 bacteria are allowed to lie in this solution for several hours it will 

 be found that at the end of this time, on subculture, they are 



••" All measurements were made at constant temperature 25° C. Resistance con- 

 stant of conductivity cell = 29 8 x 10~^. 



