COMMUNAL ACTIVITY OF BACTERIA 



255 



agar, and inspection of the figure shows that a fair growth resulted. 

 This growth was not due to an accHmatization to the dye, because 

 all experiments made looking directly toward such acclimatization 

 have been unsuccessful. Further, attempts to reinoculate gentian- 

 violet agar from this growth failed, at least insofar as the first smears 

 were concerned. 



In discussing these re- 

 sults. Churchman sug- 

 gests four possibilities: 

 The original transplants, 

 though not surviving, 

 may live long enough to 

 effect some change in the 

 dye such that subse- 

 quent transplants can 

 survive. Or, the result 

 may be due to some pro- 

 tective barrier laid down 

 by the dead bodies of 

 the bacteria. Or, nutri- 

 tional or growth-promot- 

 ing substance may be 

 provided by these same 

 dead bodies. Or, finally, 

 the results may be due 

 to communal activity of 

 the living bacteria, a possibility which will be examined later. We 

 have already discussed possible causes of survival and growth in 

 such cases in preceding chapters. 



In experimenting to find which of these possibilities actually 

 obtained, Churchman grew B. suhtilis on medium containing only 

 distilled water and agar, in order that the cells might contain a 

 minimum of nutritive material. These bacteria were washed six 

 times with distilled water and were killed. In order to test whether 

 food material was present under these conditions, these dead bacte- 

 ria were smeared over a Petri dish bottom which was then dried, 



Fig. 22. — Showing the effect of reinoculations on 

 a divided agar plate. The upper part contains gen- 

 tian violet; the lower part is plain agar. Two initial 

 strokes of Bacillus suhtilis were made. On the right 

 side, nothing further was done. On the left, reinocu- 

 lations were made on the gentian- violet agar. (From 

 Churchman.) 



