COBB'S DISEASE OF SUGAR-CANE. 



59 



cultures made at the same time yielded no better results. There was a trace of growth in 

 the mouth of the stab, but none below the surface and no spreading over the surface, not 

 even in a month's time. This failure is probably attributable to excess of sodium hydroxide, 

 since when this substance was reduced one-half by mixing equal volumes of 727 and 741 the 

 organism finally grew much better, although the growth was scanty at first. 



On gelatin made in the same way but with juice of the Common Green cane (stock 750) 

 the growth was scanty for the first two weeks, then better, but by no means copious. This 

 growth (surface) was at first rough granular, then smooth. There was no staining or lique- 

 faction (70 days). There was a beaded stab, most growth being on the surface. Streak 

 cultures developed in a similar slow manner and there was no liquefaction in them. When 

 i per cent Witte's peptone was added to this same stock there was from the start distinctly 

 more growth (several times as much), although not very copious. Subsequently there was a 

 copious growth. This was the only one of the cane- juice gelatins on which there was what 

 might be styled a good growth. The growth in the stab was better developed and the sur- 

 face growth was smooth from the start. There was no lique- 

 faction, but eventually some browning of the gelatin. In the 

 streak cultures the growth was at first reticulate-roughened, 

 then smooth, with tear-drop formations sliding down into the 

 V, where at least 0.75 c.c. of straw-yellow slime collected in 

 course of a month, but without liquefaction (fig. 34). On long 

 standing there was a feeble browning of the more exposed 

 parts of this gelatin. 



The character of the growth was quite similar in all of the 

 gelatins. Sometimes, especially when the medium was not 

 well adapted to 

 growth, the sur- 

 face was reticu- 

 late-roughened at 

 first, but the reti- 

 culations them- 

 selves, as seen 

 under the hand- 

 lens, were smooth. 

 Later the surface 

 growth became 

 smooth. In tubes 

 placed in an up- 

 right position the 

 slime collected in 



places along the streak and piled up at the bottom of the slant in a characteristic manner, 

 very well described by Greig Smith as a "tear-drop" formation (fig. 35). Some of these 

 piles were 2 mm. high. There was very little depth of slime on the rest of the streak. 

 A feeble browning of the more exposed parts of the gelatin (751) took place after long stand- 

 ing (9 weeks). In most of the gelatins there was no liquefaction. 



In one set of streak-cultures the record states that there was moderate liquefaction on 

 the forty-fourth day, but none on the twenty-fifth day ; and in one set of stab cultures the 

 nail-head settled into the gelatin slightly after some weeks. 



Fig. 33.* 



Fig. 34.f 



*Fic. 33. Colony of Bacterium vascularum on glucose gelatin. X 85. After R. Greig Smith. 



fFic. 34. Streak-cultures of Bacterium vascularum after 21 days at 18 to 23C. on cane-juice gelatin with and 

 without peptone (250 c.c. expressed juice, 750 c.c. distilled water, 10 per cent Nelson's shredded photographic gelatin). 

 Tube No. i received in addition i per cent Witte's peptonum siccum, and contained 100 times as much growth as tube 

 No. 2. On this peptone gelatin the organism showed a strong tendency to pile up and run down into the V (see fig. 35). 

 The color of the slime was straw yellow (Ridgway). There was no liquefaction. 



