22 



Scientific Proceedings (109). 



(c) Thick suspension of the Gram negative B. coli grow equally 



well on the two halves of the plate. 



(d) If very weak dilutions of suspension of the Gram negative 



B. coli be stroked across a divided plate a few colonies 

 appear on the plain agar, none at all on the gentian violet 

 agar. 



(e) From a suspension of the Gram negative B. coli, a gentian 



negative and a gentian positive strain can be cultivated. 

 (J) A thick suspension of the gentian negative strain of B. coli 



will grow equally well on the plain agar and on the gentian 



violet agar; if a weak dilution of the suspension be used a 



few colonies will appear on the plain agar, none at all on 



the gentian violet agar, 

 (g) If a thick suspension of the gentian positive strain of B. coli 



be stroked across the plate no growth whatever occurs on 



the gentian agar. 

 These observations indicate a number of the pitfalls which 

 beset those who attempt to transfer laboratory observations into 

 therapeutics. No conclusion as to the probable effect of a selective 

 therapeutic agent is justified unless the experiments on which this 

 conclusion is based have taken into consideration the quantities 

 of bacteria used. 



12 (1594) 

 The communal activity of bacteria. 



By John W. Churchman. 



[From the Loomis Laboratory, Cornell Medical School, New York 



City.] 



It has been shown above that, while B. coli like — most of the 

 gram negative organisms — is apparently uninfluenced in growth 

 by gentian violet, a careful study of thick suspension will demon- 

 strate the presence of many individuals which are susceptible to 

 the dye. 



The isolation of a strain of B. coli entirely fast to gentian 

 violet — that is to say, containing no individuals susceptible to 

 the bacteriostatic effects of the dye — has made it possible to 

 study quantitatively the reaction between this bacteriostatic agent 



