334 Mr. F. W. Twort. Fermentation of Glucosides by [Mar. 7, 



how far it could acquire a new fermenting property. After these experi- 

 ments were practically finished, my attention was directed to a paper by 

 Oscar Klotz (4), who had used the same method on one particular microbe of 

 the coli group. 



Klotz, however, only attempted to make his microbe regain characters 

 which it had lost. In this he was successful after daily sub-cultures were 

 made for about four generations, but it must be noted that his organism 

 regained its fermentative powers even when grown on ordinary agar, 

 although in this instance it was slower. The case with which Klotz was 

 dealing was really one in which certain physiological functions were lost 

 after the bacterium had passed through the body of an animal, these 

 functions being regained in sub-cultures in vitro. 



In the experiments which I have carried out the micro-organisms chosen 

 had been grown in the laboratory for some years, their origin and properties 

 being thoroughly well known. Many of them were obtained directly from 

 Dr. MacConkey. 



The media used in the experiments contained a sugar which the particular 

 microbe is ordinarily unable to ferment. The sugar was added to ordinary 

 salt peptone water to the extent of 2 per cent. 



To ensure that the cultures were pure, they were first plated out, sub- 

 cultures being obtained from single colonies. These sub-cultures were then 

 passed through the usual sugar tests, being grown for four weeks at 37° C. 

 Each culture so obtained and proved to be pure was transferred to a medium 

 containing the sugar which at first it had failed to ferment. In such 

 a medium it was allowed to grow for 14 days, when sub-cultures were again 

 made to the same sugar medium and so on for successive generations. 



All the sub-cultures were incubated for four weeks, the experiments being 

 prolonged over months. The reason why the cultures were incubated for 

 14 days was to try to induce the microbe to attack the sugar after it had 

 used up the other nutritive material in the medium. If division was still 

 going on, it was assumed that any variety with a tendency to ferment the 

 particular sugar would survive and multiply, since it could utilise the latter 

 which the other members of the culture could not. In this way it might be 

 expected that in successive generations a culture of increasing fermentative 

 power would be obtained. 



Such indeed proved to be the case ; for several microbes were ultimately 

 able to attack sugars which they, in accordance with universal bacteriological 

 experience, at first failed to do. This change of function was slow, in most 

 cases many successive generations being required before the new property 

 was fully developed. Thus all the members of the para-typhoid sub-group 



