258 



ANIMAL AGGREGATIONS 



determine whether the observed facts were to be explained by the 

 relation of the number of organisms to the amount of gentian violet 

 to which they were transferred. This is the same sort of relationship 

 which Allee and Schuett found effective with various organisms ex- 

 posed to colloidal silver, and which Carpenter found in the case of 

 fishes exposed to lead nitrate. In the language of the original report: 

 "Large inoculations of this gentian-negative strain grow in the 

 presence of gentian violet without any apparent restraint; so, too, 

 do inoculations of 30 cells; whereas single cells, under identical 

 conditions, do not grow at all. This might be due to the fact that 



35 



50 



60 



Fig. 24. — Showing effect of size of transplant on amount of growth of a gentian- 

 tolerant strain of Bacillus coli on gentian-violet agar. Numbers in the test tubes give 

 the number of cells transplanted. (Redrawn from photograph published by Churchman 

 and Kahn.) 



groups of cells, even small groups of 30 individuals, were able to 

 make some change in the dye, gentian violet being assumed to offer 

 a slightly unfavorable medium even for this gentian-negative strain, 

 in spite of the absence of any apparent inhibition to the growth of 

 groups of cells. Single cells might be unable to effect this change in 

 dye in sufficient amount to allow growth to take place." 



Acting on the assumption that this reasoning is correct and on 

 the knowledge that the single-cell transplants had been made into 

 5 cc. of 1 : 100,000 gentian- violet broth in which i cell would not 

 grow while 30 cells transplanted together would do so, transplants 

 were made of 30 cells into 150 cc. of this broth. Growth occurred 

 with a fair degree of constancy. Even when 30 cells were transplant- 

 ed to a liter of such broth, growth took place in 60 per cent of the 



