25 



der of the 10 c. c. of gelatin was unchanged, the stab fading- out in the 

 depths to scattered round white colonies. 



It would seem, therefore, that excess of malic aid favored liquefac- 

 tion and the production of the yellow pigment. PossiI)l\% however, 

 these results are to l)e ascribed solely to changes in the physical char- 

 acter of the gelatin. The melting point was slight!}' reduced by the 

 addition of the acid and was lowest in the stocks which received 

 the most acid. 



The most growth obtained on any gelatin was with +54 malic acid 

 gelatin to which 10 per cent of cane sugar had been added. This was 

 a slant culture kept in the ice chest at 10° to 25° C, for 6^ months, 

 during all of which time it was overlooked, so that if there was any 

 retardation of growth at iirst, there is no record of it. When exam- 

 ined at the end of 6i months, there was a most copious growth, but no 

 trace of liquefaction. At some time during the summer the ice was 

 allowed to get low and the gelatin melted, allowing a copious bright 

 yellow surface growth to fall to the bottom. Subsequent!}^, with the 

 addition of more ice, the gelatin resolidified and a new surface growth 

 formed. When examined at the end of the 6^ months, there was a 

 dense bright yellow rim 12 to 15 mm. wide, and a copious surface 

 growth separated from the yellow precipitate, already mentioned, by 

 a mass of solid gelatin free from browning and clear, except for tiny 

 scattered masses of bacteria imprisoned when the gelatin resolidified. 

 The bright yellow surface slime was still alive. 



In the +4:8 gelatin with 5 per cent cane sugar, at the end of 40 days, 

 at 8° to 20° C. (mostly under 15° C), there was a compact bright yel- 

 low surface growth, 12 mm. in breadth and a distinct stab, but no 

 liquefaction. This experiment was repeated at 12° to 20° C, using 

 both +48 and +54 gelatin with 5 per cent cane sugar and continuing 

 the experiment 30 days. During this time there was no liquefaction 

 whatever in the +54 gelatin and only a very feeble liquefaction in the 

 +48 gelatin, i. e., the distinctly yellow surface growth, 5 or 6 mm. in 

 diameter, was sunken in slightly. In another experiment with +48 

 and +54 gelatin with 10 per cent cane sugar, kept at 7° to 21° C. 

 (most of the time above 14° and below 19°), there was no liquefaction 

 in 49 days. 



The same results were obtained with gelatin (stock 244c), to which 

 10 per cent cane sugar was added. After fJl days at 15° to 20° C. 

 there was no liquefaction whatever in one tube and only the very 

 slightest in the other, and no brown stain in either. The growth was 

 better than in tubes of sugar-free gelatin which liquefied. 



There can be no doubt, therefore, that, while powerfully stimulating 

 growth, cane sugar in small doses retards and in large doses entirely 

 inhibits the liquefaction of the gelatin, whether the medium is acid or 

 alkaline. 



