376 



Variation in Bacillus coli. 



quite normal and strong at 37° C. and was quite strong at 20° C, there being 

 only a great tendency to delay in development. In every case before testing 

 in the various peptone waters a strong growth was first obtained and heavy 

 inoculations were used, and there was no trace of the dye stuff added to the 

 test media with the culture. The effect which was produced in each case 

 described above had been brought about by some impression made on the 

 protoplasm as it was transmitted unchanged through successive cultivations 

 on ordinary media. 



The point which stands out clearly from the above results is that, from an 

 original typical culture of B. coli obtained from a single cell, two strains 

 have arisen, (1) a strain slightly modified by the dye stuff, but in a permanent 

 manner and refusing to be further affected ; (2) a strain gradually under- 

 going profound and increasing change in the same environment and resulting 

 in an organism entirely different from the original culture, the strain being 

 also of a permanent character. 



It is important to notice that from one original organism there have arisen, 

 by a simple process of cell division, at least two organisms, one of which is^ 

 practically resistant to its environment, while the other has become greatly 

 and progressively modified. It has been held that all such individuals 

 should behave alike under similar circumstances, but it has been my constant 

 experience that this is not the case. Failure to recognise this has no doubt 

 led to the impression that organisms do not show variation. 



Further, granting that these fermentative changes are brought about by 

 enzymes present in the bacterial cell, it is evident that these are not an 

 intrinsic and integral part of the protoplasmic substance. They may be 

 entirely lost or greatly modified in activity, and, supposing that two enzymes 

 at least are necessary to bring about the complete fermentation of the test 

 substance, it is also evident that those which bring about the acid change- 

 may subsist while those which produce gas, etc., are completely lost. 



Under these circumstances, it is not too much to suppose that in the life of 

 the organism itself, the opposite phase may occur, and that, as under certain 

 circumstances fermentative power is lost, so also, under some other set of 

 circumstances, it may be acquired when it does not already exist. 



