56 



will be brought out to best advantage b}' comparison with Ps. cain- 

 pestris or Ps. jphaseoU, both of which exert on starch a very powerful 

 diastasic action. When either of these germs is grown on potato cyl- 

 inders in water for 30 days, not simply all of the starch in the surface 

 cells, but also all of that in the deeper parts of the cylinder, is acted 

 upon, and this action is not feeble, but so vigorous and far-reaching that 

 if the whole cylinder is crushed in a large bulk of the iodine water 

 there is either no color reaction whatever, or merely in places a feeble 

 brownish-purple tinge, indicating that all of the starch, or almost all, 

 has been converted. 



Growth on Potato with Addition of Cane Sugar. 



These cylinders were the ordinarj^ potato cultures in test tubes, to 

 each of which was added 1 gram of cane sugar. At first growth was 

 retarded — e. g. , on the fourth day it was slight and white or nearly 

 white. On the thirty-seventh day it was yellow, extended down into 

 the fluid, and was 20 to 25 times as abundant as in the check tubes. 

 The surface was wet-shining, but not smooth, owing to the protrusion 

 of rounded zoogloeai. On the sixty-seventh da}" the slime was wax yel- 

 low, and covered the whole cylinder, just as Ps. campestris or Ps. 

 phaseoli would have done without the addition of sugar. The entire 

 culture now looked like shagreen from inequalities in its surface due 

 to the protrusion of rounded masses. The slime was neutral, or at 

 least not alkaline, and the small amount of fluid remaining in the bot- 

 tom of the tubes was plainly acid to neutral litmus paper. The brown 

 stain of the fluid was less than in the check tubes. 



Growth on Potato with Addition of Maltose and Dextrine. 



This medium consisted of potato cylinders standing, two-thirds cov- 

 ered with distilled water, in well-plugged test tubes. To each tube 

 was added 100 milligrams of maltose and an equal quantity of dex- 

 trine. They were then re-steamed as usual (20 minutes at 100'-' C, on 

 3 consecutive days), constituting stock 301. Each tube was inoculated 

 with a large loop of Ps. hyacinthi from a well-clouded beef-broth 

 culture 11 days old, check tubes made from the same tuber being held 

 for comparison. 



Result. — During the first few days (4 at least) there was not as 

 much growth in the 2 maltose-dextrine tubes as in the 2 check tubes. 

 However, at the end of 24 days (temperature 19° to 25° C.) there was 

 an abundant yellow, wet-shining growth over the whole of the exposed 

 part of the cylinder, down into the upper part of the water, and on 

 the wall of the tube, at least 15 times as much growth as in the check 

 tubes. This growth continued for several weeks. 



