LABORATORY AND GREENHOUSE STUDIES. 



69 



In dextrose plus KNO3, originally +5, the culture became +8, this 

 also showing less growth (and less aci.d) in the absence of peptone. 



Cultures in peptone plus rosolic acid made good growth but did not 

 affect the color. Cultures in peptone plus rosolic acid plus dextrose 

 clouded well and changed from the pink color of the check to a sort 

 of orange yellow, thus indicating the production of an acid. 



Cultures in peptone plus neutral red grew well and changed the 

 color of the medium to an orange yellow, in this case showing a slight 

 production of alkali. In cultures containing peptone plus neutral red 

 plus dextrose the growth was good and the color changed to a ma- 

 genta, thus indicating the production of an acid. 



A series of cultures was made in Dunham's solution colored with 

 litmus, some of the tubes containing grape sugar and others without 

 any sugar. Those containing the sugar in three days became well 

 reddened and partially bleached. Those without the grape sugar 

 became well clouded and showed good growth, but did not change in 

 color from the check. 



The amount of gas produced in media containing dextrose is shown 

 in Table VII. 



Table VII. — Amount of gas (in millimeters) produced by various cultures in different 



media, experiments 1,2,3, and 4- 



The failure of some of the cultures to produce gas in experiments 1 

 and 2 while they readily produced it in experiments 3 and 4 is rather 

 striking and not readily explainable. Occasionally, in subsequent 

 experiments not noted here, a similar failure of a certain culture to 

 produce gas in dextrose has occurred. From further cultures of 

 descendants of such a culture, however, it is evident that the same 



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