COMMUNAL ACTIVITY OF BACTERIA 249 



rial into the new medium before maximal growth can occur. The 

 fact that with bacteria, as we have already seen with Protozoa 

 (chap. X), transfers from cultures during periods of maximal growth 

 do not exhibit a lag period shows that such secretion is not always 

 essential. Robertson's work (1924) for Protozoa and that of Valley 

 and Rettger (1926) for bacteria indicate that it may at times have 

 significance. 



b) The adaptation theory is based on the idea that acclimatization 

 to a new medium requires time. The evidence mentioned above 

 shows that this is not always true; further, transfers from old cul- 

 tures may show lag even though they are transferred to the same 

 medium. Fulmer (1921) presents evidence that adaptation may be 

 operative in the case of the transfer of yeast to a medium containing 

 ammonium fluoride. 



c) The non-viability theory which supposes that some of the or- 

 ganisms die off early may still hold for Protozoa, although it does not 

 hold universally for bacteria, since culturing on agar plates reveals 

 the lag phenomenon and non-viable bacteria would never be counted 

 in this method. 



d) The agglutination theory suggests that bacteria agglutinate on 

 the plates, and the resulting count is of clusters of bacteria rather 

 than of individuals. This may be true under certain conditions, but 

 lag can be shown when agglutination has been avoided. 



e) The theory of recovery from injury holds that exposure to the 

 accumulated products of metabolism in the parent culture affects 

 the different cells so that time is required to recover when placed in 

 a new environment. Buchanan and Fulmer regard this as perhaps 

 an "approximation of the truth, though probably not entirely ade- 

 quate." If we cannot admit that the production of such toxic sub- 

 stances is universal, we may still think of the injury as being due to 

 starvation in the deteriorated parent culture. Somewhat the same 

 idea is expressed in the inertia theory, which holds that the trans- 

 ferred organism continues to grow for a time in the new medium as 

 it would have grown in that from which it was taken. Buchanan's 

 so-called germination theory of lag appears to be another statement 

 of about the same concept. 



