CHAPTER II 



CONDITIONS MODIFYING THE CHAKACTEES 

 OF BACTEEIA 



The factors which appear to influence the growth and de- 

 velopment of bacteria and to produce modification in their 

 characters are many in number and diverse in nature, and it 

 is often impossible to state with certainty which of these 

 various factors is the one primarily responsible for the 

 modification observed in a particular case. 



1. Many variations appear to be sponta/neous, not due, 

 that is to say, to any external agency, but the result of 

 developmental or atavistic tendencies inherent in the organism 

 itself. We know as little of the nature of these tendencies to 

 variation as we know of the nature of those which control 

 normal development and, in the vast majority of cases, prevent 

 variation occurring. 



Some spontaneous variations are examples of "pleoTnorph- 

 ism" and represent stages in the life history of the individual 

 organism or of the race. Others cannot be explained in this 

 way. For example, one component of a diplococcus may retain 

 a stain while its fellow fails to do so. In such a case faulty 

 technique cannot be held responsible, nor can the variation be 

 attributed to differences in environment. Moreover in the 

 case of the meningococcus it has been found to persist after 

 animal passage (McDonald, 1908). The variation would appear 

 to date from the cell division which constitutes the "birth" 

 of the organism. Denny (1903) observed the same inequality 

 in staining properties in different segments of a segmented 

 form of B. Xerosis. 



Many other examples of spontaneous variation will be 

 found in later pages. 



2. Differences in characters are sometimes associated with 

 differences in geographical distribution. Thus Schultz (1909) 



