11 



gelatin. Gelatin was made up in bulk and distributed to a series of 

 flasks. One per cent, of carbohydrate was added to each flask, and the 

 gelatin in the flasks was poured into tubes of equal diameter, so that 

 each tube contained gelatin to a depth of 50 m. m. After sterili- 

 zation, each tube was inoculated with the organism to be tested by 

 spreading a suspension of the organism over the surface of the gelatin. 

 The tubes were then placed in the incubator, kept at 22 C and allowed 

 to remain for thirty days. At the end of the incubation period, the 

 amount of liquefaction was determined by measuring the depth of the 

 gelatin which had been reduced to a liquid state. 



The results of the experiments are given in the table which follows. 



Table No. 5. 



Table showing the amount of liquefaction in millimeters in carbo- 

 hydrate gelatin by members of the Proteus group. 



The table shows that dextrose, saccharose, levulose, mannose, galac- 

 tose, maltose , and raffinose, tend to inhibit the .liquefaction of gelatin 

 by all strains of P. vulgaris and by P. mirabilis, 3 and 17, while 

 gelatin containing lactose or mannite do not retard the liquefaction of 

 gelatin. All of the strains of P. Zenkeri, P. Zopfi i, and mirabilis, 

 with the exception of P. mirabilis 3 and 17, did not liquefy gelatin 

 in any of the tubes, even when allowed to remain in the incubator for 

 three months. It was found that sugars which inhibited the gelatin 

 liquefaction by Proteus vulgaris were fermented by that organism. 



To find out whether acid was produced by the fermentation of the 

 sugars in the gelatin tubes, a second series of sugar gelatin tubes were 

 prepared and a few drops of 1/ solution of azolitmin were added to 

 each, as well as to the nutrient gelatin control. The tubes were inocu- 

 lated with P. vulgaris as in the previous experiment and incubated 

 at 22 C. In every tube which showed liquefaction, the litmus remained 



