CHAPTER XV 

 COMMUNAL ACTIVITY OF BACTERIA 



Many of the relationships which we have found to hold for animals 

 can also be studied with bacteria. The large amount of work done 

 upon these micro-organisms and the excellent technique developed 

 both in culturing and in making isolations cause the results obtained 

 to be the more significant for our studies. In one way bacteria as 

 presented here and spermatozoa as discussed in the following chap- 

 ter may serve as test cases for us. The situation may be stated thus: 

 We have been presenting certain evidence concerning the role of 

 numbers of individuals present in relation to the physiology of each 

 individual. The studies so far have dealt with a wide range of ani- 

 mals. If we turn to some totally different organisms, such as the 

 bacteria, shall we find similar relationships prevailing there? If we 

 do, and if we also find the same conditions holding for the sperma- 

 tozoa, we shall have the greater reason for regarding the phenomena 

 we are studying as being of universal biological significance.' 



Buchanan (191 8) has summarized the life-cycle of a bacterial 

 culture into seven periods. These are illustrated in Figure 21, where 

 each phase extends to the left of its respective numeral. This analy- 

 sis of conditions in a bacterial culture is essentially like that known 

 to obtain for many protozoan cultures (cf. Fig. 9) except that the 

 analysis with bacteria has been more carefully made. The different 

 phases will be discussed briefly here. 



I. The initial stationary phase covers the time during which the 

 number of introduced organisms shows no increase. This phase has 

 been studied but little. If the bacteria are actively growing at the 

 time of transfer, growth may continue on the new medium, indicat- 



' Two summarizing books have appeared dealing with the material presented in the 

 early part of this chapter, by Buchanan and Fulmer (1928) and by Henrici (1928). 

 These assist a layman in this field to present a more seasoned summary than would 

 otherwise be possible. 



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