372 Probable Value to B. coli of " Slime " Formation in Soils. 



experimental organism did not usually grow in a typical manner, but in 

 large watery colonies, which were at first not recognised as B. coli, and 

 were also soon involved with other growths on account of their spreading 

 nature. It was therefore necessary to employ the usual method of pre- 

 liminary inoculation into bile-salt glucose broth, followed by plating out 

 into ordinary ( + 1), or bile-salt agar. In this way B. coli was always 

 readily isolated, but the tendency to form large, moist, slimy colonies was 

 still marked, a characteristic to which I have directed attention before. 



The results were not of any great interest from the point of view of 

 variation. From time to time, during the first 18 months of the investigation, 

 apparently typical coli were isolated which refused to grow in peptone water 

 or to attack any of the test substances. In many cases, the original culture 

 from the plate failed to attack dulcitol and sometimes mannitol, but these 

 failures were not of a permanent character. Towards the end of the experi- 

 ment quite typical organisms only were obtained. The necessary use of bile- 

 salt broth possibly is adverse to the separation of atypical organisms in the 

 presence of a preponderance of typical forms. There was not apparently 

 during the whole course of the experiment (which lasted three years) any 

 marked diminution of the original B. coli, as it could be recovered in all cases 

 from at least O'OOOOl grm. of the soil. 



The remarkable point of the investigation lies, however, in the fact that 

 throughout the course of the experiment no further addition of water was 

 made to the flasks. The control flasks, which did not contain B. coli (though 

 all the other soil organisms were present), dried up within a few months of the 

 start. In all the flasks which contained B. coli not only did the flasks retain 

 their moisture for three years, but during the first 12 months of the experiment 

 had evidently taken up large quantities of moisture from the atmosphere, 

 and in one or two instances the soil became completely water-logged. 



It seems evident that this extraordinary behaviour is connected with the 

 B. coli, and in view of the fact, which I have constantly noticed, that this 

 organism can easily produce " slime " (without the presence of sugar), and 

 that when grown in this manner in soil it certainly does so, it seems 

 reasonable to attribute the water-absorption of the soil to this curious 

 property. These results possibly give at the same time some explanation of 

 the well-known power of many organisms which occur in soil, especially the 

 " nodule " bacteria, to form " slime." 



The viability of B. coli for such a long period is also remarkable, but 

 cannot, of course, be taken as true for ordinary soils, as there are bactericidal 

 influences at work in such, which have been destroyed by the initial sterilisa- 

 tion necessary in these experiments. 



