VARIATION IN UNICELLULAR ORGANISMS 113 



latter make no use of it, for several or many generations. But 

 in the course of time some of them develop the power to split 

 up this sugar and to thus obtain nutriment from it. They 

 thereupon begin to multiply and flourish greatly. And such 

 individuals transmit this nevi^ly acquired power to their 

 descendants for a great number of generations, even though 

 the descendants may live where there is none of the sugar 

 that induced the change. 



Many examples of this type of change could be cited ; and 

 many other phenomena of extraordinary interest for genetic 

 variation are known in the bacteria. Instead of being patterns 

 of uniformity and constancy, as was supposed, it is now found 

 that bacteria develop genetic variations, inherited changes, 

 with great frequency and in great variety. The technical 

 worker who endeavors to keep his conditions constant by 

 employing cultures of a single strain of bacteria is dismayed 

 to find that his single strain has broken into two or more, with 

 diverse physiological properties. Particularly are the bacteria 

 genetically sensitive to changed environments; these induce 

 new inherited characteristics; so that the "inheritance of 

 acquired characteristics" is a characteristic feature of genetics 

 in these organisms. 



It must be said that the phenomena of genetics and genetic 

 variation are by no means fully worked out in the bacteria. At 

 present there is much difference of interpretation as to some 

 of the phenomena. In some quarters we read of free bacterial 

 genes that circulate about in nature and that may become 

 associated with various bacterial stocks, changing their heri- 

 table characteristics; and other adventurous views are put 

 forth.* When these matters are fully cleared up, they will 

 beyond doubt yield a most important chapter in genetic 

 science, and particularly in genetic variation. In any case, the 





