254 ANIMAL AGGREGATIONS 



of single cells to new media, gives a proper method for attacking 

 this problem. This technique was employed by Churchman and 

 Kahn. They took their transplants from a strain of B. coli which 

 had been isolated from a single colony growing on gentian-violet 

 agar and kept growing by frequent transplants for several weeks on 

 media containing that dye. 



Care was taken to avoid as much as possible the lag phenomenon. 

 When strokes of a heavy suspension were made on gentian-violet 

 agar, growth occurred with almost no inhibition; but transplants 

 of single cells almost never grew, although only motile organisms 

 were picked for transfer. Single transplants to controls lacking the 

 dye gave as high as 85 per cent growth. "In the two cases in the 

 whole series of cell transplants in which growth occurred, marked 

 delay took place, a delay which was never observed for the controls. 

 Moreover transplants of small groups of organisms (five to fifteen) 

 did not grow, though transplants of thirty individuals grew regu- 

 larly." 



Churchman in another series of experiments, using Bacillus suh- 

 tilis, which is definitely susceptible to gentian violet, tested the ef- 

 fects of repeated inoculations on the ability of this organism to grow 

 in the presence of this dye. The susceptibility of B. suhtilis is shown 

 by the fact that its growth is prevented by dye dilutions of i : 1,000,- 

 000; inhibited by 1:2,000,000; and only becomes vigorous at dilu- 

 tions of 1:3,000,000. "If, however, the gentian violet half of the 

 plate is repeatedly and heavily inoculated on successive days at the 

 same place, a fair growth— in some cases a rather vigorous growth — 

 may finally be obtained." Such an experiment is shown in Figure 

 22. The figure shows the results of two initial strokes of a thick sus- 

 pension of B. subtil is on this divided plate, the lower half of which 

 is plain agar while the upper half is gentian-violet agar, at a strength 

 of 1 : 100,000, which is ten times stronger than a dilution known to 

 prevent growth. 



After the first stroke, nothing further was done to the right-hand 

 side, and the usual effect of the dye is clearly shown by the lack of 

 growth on the gentian-violet part of the plate. On the left-hand 

 stroke organisms were repeatedly introduced on the gentian-violet 



