COMMUNAL ACTIVITY OF BACTERIA 253 



Kahn (1921) and of Burnet (1925). It is presented in some detail 

 both because the results broaden the base of our knowledge of the 

 physiological effects of numbers, extending this to the bacteria, and 

 also because these results have been attained independently of simi- 

 lar work on different material. Verification studies are much more 

 impressive when carried on in a different laboratory from that 

 bringing out the original report ; and when many different investiga- 

 tors working in widely separated laboratories and on radically dif- 

 fering materials reach similar conclusions independently and about 

 the same time, the fundamental nature of the phenomenon under 

 discussion becomes the more striking. 



The bacterial studies in question are concerned with the behavior 

 of certain types of bacteria in the presence of gentian violet. Bacil- 

 lus coli grows equally well on both sides of a divided agar plate, 

 one-half of which contains gentian violet, provichng both sides are 

 stroked with a heavy suspension of the bacteria. As the strokings 

 are made with increasingly dilute suspensions, the colonies become 

 less numerous on the gentian-violet side and finally disappear com- 

 pletely. In part the results may be due to differential susceptibility 

 to the dye, shown by different B. coli individuals, for if a plain agar 

 plate is inoculated from broth cultures of this bacterium which 

 have been exposed to gentian violet, the stained organisms appear 

 to grow as well as the controls, but if the experiment is repeated 

 with increasingly dilute suspensions of B. coli, it will be seen that 

 many of the bacteria have not survived the treatment with the 

 stain. 



Such results are what might be expected from the well-known 

 relations between growth and size of the inoculum. In an ordinary 

 bacterial culture, many organisms are known to be dead. Others, 

 though living, are more readily affected by the somewhat unfavor- 

 able conditions found in the new medium to which they are trans- 

 planted, which makes it much more probable that heavy growth 

 will occur if the inoculum consists of thousands or millions of organ- 

 isms than if it contains merely hundreds. The fact just observed con- 

 cerning the better growth of a large than of a small inoculum exposed 

 to gentian violet becomes merely the starting-point of our interest. 



The technique developed by Barber, which allowed the transfer 



