Electric Potential of Bacterial Suspensions. 151 



it is grown, that is, a microorganism incapable of growing in the 

 presence of gentian violet readily does so on a more suitable 

 medium, and it can adapt itself to a less suitable medium if 

 started on a selective medium. Gentian violet has not been 

 found to be of any value in the differentiation of the Mucosus 

 capsulatus group. Further, the microorganisms of this group 

 which refuse to grow on agar violet are representatives of what 

 we at present regard as three distinct species. 



It would seem from the result of the experiment here recorded 

 that while the action of gentian violet on bacteria is usually 

 constant, it is sometimes susceptible of modification and may not 

 be as fundamental a characteristic as originally supposed. 



97 (793) 



On the influence of light on the electric potential of bacterial and 

 other suspensions. 



By S. W. Young (by invitation). 



[Laboratory of Physical Chemistry, Stanford University, CaL] 

 Experiments in this laboratory have shown that light and other 

 forms of radiant energy exert a marked influence on the rate of 

 wandering in the electric current. Thus the rate of wandering 

 of arsenic sulphide suspensions is about twice as great in the dark 

 as under strong illumination in the sun, or in the carbon arc or in 

 the Nernst lamp. On the other hand, the rate of wandering of 

 mastic emulsions is increased under strong illumination, and that 

 to the extent of about forty per cent, of the value in the dark. 

 Ferric hydroxide is retarded in the light to the extent of about six 

 per cent., while chlorophyll suspensions are accelerated in the 

 light to the extent of about forty per cent. The effect of the 

 radiant energy is not in general instantaneous, but requires a 

 few minutes exposure to reach its greatest value. In general also 

 the effect is reversible, that is colloids whose rates of wandering 

 have been influenced by radiant energy, return to their original 

 values if kept in the dark for some minutes. 



These phenomena are very interesting in connection with 

 photochemical reactions in general. Arsenic sulphide suspensions 



