Selective Action of Gentian Violet. 



21 



growth whatever will ever occur on the gentian violet side of the 

 plate. The organism will, indeed, refuse to grow up to the dividing 

 line between plain and gentian violet agar, ceasing sharply at a 

 point about 1 / 2 to I cm. from this line. 



If, however, the gentian violet half of the plate be repeatedly 

 re-inoculated with thick smears, a moderate growth — in some 

 instances a fairly vigorous growth — occurs. This is not due to 

 acquisition by the bacteria of resistance to the dye, for if the 

 organisms, which have thus grown, be transplanted to gentian 

 violet agar they will not grow in the presence of the dye. Nor is it 

 due to insufficiency of dye, for in the plates used in the experiments 

 dye was used in strengths greatly in excess (1-100,000) of the 

 strength necessary to prevent the growth of B. subtilis (1-1,000,- 

 000). 



The explanation of the phenomenon is not at present perfectly 

 clear, but there is some reason for believing that it may be due to 

 a property of bacteria — not hitherto recognized — of communal 

 action. A few studies of single stained bacterial cells, made by 

 the method of Barbour, lend support to this explanation. 



11 (1593) 



The selective action of gentian violet in relation to chemotherapy. 



By John W. Churcmhan. 



[From the Laboratory of Bacteriology, Cornell Medical School, New 



York City.} 



It is clear from the facts stated in the four previous communica- 

 tions that selective bacteriostasis is a complex process. The 

 method of divided plates presents a perfect machinery for studying 

 the workings of this process; and in the selective property of 

 gentian violet we have a means of observing the various elements 

 of the process under perfect control on a single plate. On such a 

 plate we will find that 



(a) Thick suspension of the Gram positive B. subtilis will not 



grow in the presence of the dye. 



(b) By repeated re-inoculations of this organism a moderate 



growth can be procured on the gentian violet agar. 



