168 MASS. EXPERIMENT STATION BULLETIN 167. 



Table VIII. indicates that flasks 5, 6, 7 and 8 proved to be positive 

 from the beginning, while all others were negative, except flask 9, which 

 test gave negative results before forty-eight hours, then became positive. 

 This change may be attributed to inhibitory action. 



Determination of the Rate of Growth. 



It was found desirable to determine the rate of growth as well as the 

 different hydrogen ion concentrations. This was done by comparing 

 growth turbidity. 



Immediately after inoculation, 10 cubic centimeters of the contents of 

 each flask of the set 1 to 13 was transferred into a corresponding set ^ of 

 test tubes of uniform diameter. These test tubes were kept as the standard 

 by the addition of thymol, and protected from evaporation by means of 

 rubber stoppers. At each determination the same amount of a well- 

 mixed sample was transferred from each flask mto another set of corre- 

 sponding test tubes, and the turbidity compared with the standard. The 

 results are here recorded. 



— no growth. 

 + slight growth. 



++ strong growth. 

 +++ abundant growth. 



Table IX. indicates that after twenty-four hours a fairly strong growth 

 took place in flasks 6 and 7, and slight growth in flasks 5 and 8. It was 

 after forty-eight hours that the growth was first observed in flask 9. All 

 other flasks proved to be negative. 



' It was necessary to prepare a separate standard for each flask, because flasks 4 and 5 became 

 turbid on addition of acid, as previously stated. 



