Nov. IS, I9I9 Bacterial Blight of Soybean 185 



Nitrate bouillon. — Nitrate bouillon cultures in fermentation tubes 

 gave good clouding in the open arm but none in the closed arm. No gas 

 was produced. In all cases there was a definite line of demarcation 

 across the U of the tube. There was a fair positive test for ammonia 

 and a strong positive test for nitrates. No nitrites were found. The 

 medium in the open arm became so dark brown in color that it was im- 

 possible to test with any degree of accuracy for acidity. 



Fermentation tubes. — The tests were made in 2 per cent Difco 

 peptone water and 2 per cent of each of the following carbon com- 

 pounds: Dextrose, lactose, saccharose, maltose, glycerin, and mannit. 

 Clouding was first obser\'ed at the end of 24 hours. In a week good 

 growth had developed in all tubes in the open arm. With all of the sugars 

 except dextrose, considerable cloudiness developed also in the closed 

 arm, but no gas was found in any tube. Tests proved that there was 

 growth in the closed arm of the dextrose culture tubes also; but here 

 it was more or less slimy, and clear rather than cloudy. Bacterium coli 

 was used as the control in this test, and gas was produced in all Bact. coli 

 tubes. 



When the cultures were 2 weeks old they were titrated, and they 

 were tested again at the end of five weeks. Phenolphthalein was used as 

 the indicator, and in every test there was preliminary boiling to drive off 

 the carbon dioxid. At the end of two weeks the maltose, lactose, glycerin, 

 and mannit cultures showed considerable increase in alkalinity. When 

 5 weeks old, however, the tests showed that acid was being produced 

 again, and in some instances the cultures were more acid than the con- 

 trols. The maltose and lactose cultures had turned so dark brown in the 

 open arm that it was difficult' to determine the exact endpoint in the 

 titrations, but several trials made from each tube where the medium was 

 not so dark-colored gave a satisfactory check on the results. 



After two weeks' growth the dextrose and saccharose cultures showed, 

 in general, increased acidity. In a number of instances, however, the 

 tests made from the closed arms indicated an increase in alkalinity there. 

 At the end of the 5-week period all the cultures showed an increase in 

 acid in both open and closed arms. 



The condition just described, which at first glance looks a bit confusing, 

 may be explained by the following theory: The organism grows very 

 rapidly in the dextrose and saccharose solutions where it at first causes an 

 alkaline reaction, followed by the production of acid. The change does 

 not take place so rapidly in the closed arm, and for this reason titration 

 after two weeks still showed increased alkalinity. The open arm had 

 gone beyond this point, and acid was being produced there in excess. 

 Gradually, as we have seen, the acid condition became general tliroughout 

 the tubes. No doubt the same action took place in the lactose, maltose, 

 glycerin, and mannit cultures already described, except that there the 

 changes occurred more slowly. 



