BEGINNINGS OF CO-OPERATION 67 



tection is in fact in this case an expression of calcium 

 physiology. The further developments on the sub- 

 ject await exact information concerning the details 

 of the physiological effects of calcium. 



It is probably of more direct human interest to 



■;V*i.;::i: 





%^ 





35 



50 



60 



Fig. 7. Bacteria frequently do not grow if inoculated 

 in small numbers; here different numbers of Bacillus 

 coli were inoculated into a medium containing gentian 

 violet. 



know that under many conditions bacteria will not 

 grow if only a few are inoculated into an animal, 

 man for example; while with a larger inoculation 

 they may grow abundantly. (33) Gentian violet is a 

 poison for many bacteria and in regular medical use 

 for that purpose. In one well-studied case (Figure 7) 

 bacteria belonging to the species Bacillus coli failed 

 to grow on agar containing gentian violet, if singly 

 inoculated on it; only when thirty or more bacteria 



