COBB S DISEASE OF SUGAR-CANE. 



57 



Witte's peptone 15, cane-sugar 15, agar flour 4.5, autoclaved for 15 minutes at 1 10 C. The 

 surface growth was wet-shining and about a cubic centimeter of pale yellow slime accu- 

 mulated in the V of each tube. 



The growth on potato-agar was somewhat better than on beef -agar; there was a smooth, 

 wet-shining, yellow streak (fig. 32), varying from scanty to abundant. 



On litmus-lactose-agar there is a very scanty to moderate growth, with slow but dis- 

 tinct bluing and no reduction of the litmus. No acid is formed. 



On Hunger's agar (Mr. Johnston's notes) there is a very noticeable difference in the 

 growth, depending on whether the monobasic or dibasic phosphate is used. When the 

 monobasic (acid) salt is used there is a growth rather light yellow in color, while with the 

 dibasic salt it is rich yellow with 

 paler edges, and is much more 

 luxuriant, although not heaped 

 up as in the case of Bacterium 

 fhaseoli. 



Greig Smith gives the fol- 

 lowing description of the organ- 

 ism in glucose-gelatin plates : 



The colonies develop slowly. 

 In 7 days at 22 C. they are i mm. 

 in diameter, and appear as small, 

 raised, viscid drops. When mag- 

 nified 6o-fold [see fig. 33] they 

 appear round and uniformly gran- 

 ular, like a thin yeast colony, the 

 deep colonies like those upon the 

 surface. In 20 days the colonies 

 reach a diameter of 4 to 8 mm. and 

 look like drops of yellow beeswax. 

 The medium shows no signs of 

 liquefaction, but when the colony 

 is scraped or washed off a pit is 

 revealed. 



Growth in the absence of 

 glucose is similar but much 

 slower (RGS.). Fig. 31.* 



In cane-juice gelatin-stabs 



there is a smooth, piled-up, restricted yellow surface growth. There is no liquefaction 

 (possibly in some instances there was an unobserved slight liquefaction, i. e., a sinking in 

 of the nail-head), no production of gas, no stain, and no formation of crystals. Greig 

 Smith reports slow growth on gelatin in the presence of cane-sugar or fruit-sugar at a 

 temperature of 30 C. or under. In a gelatin stab (stock i.ooof), inoculated from a young 

 culture on litmus lactose agar and kept mostly at 22 to 24 C., there was at the end of two 

 days a yellow, wet-shining, restricted (piled-up) surface growth and a needle-track best 

 developed in the top layers of the gelatin. There was no liquefaction in 20 days. The 

 surface growth remained piled up and restricted. Separate colonies were visible only in 

 the lower part of the stab. No crystals appeared, no stain, no gas. 



In six tubes of nutrient gelatin composed of 100 distilled water, 10 gelatin (Nelson's 

 photographic No. i), 0.5 Witte's peptone, 0.5 dipotassium phosphate, and 0.02 malic acid, 



*FlG. 31. An agar-poured plate of Bacterium vascularum (a pure culture) 1 1 days old. Plated from the interior 

 of plant No. n. Photographed April 27, 1903. 



fA +15 gelatin containing beef-broth, Witte's peptone, 10 percent Nelson's No. i gelatin, and sodium hydrate. 



