32 



and very little or none at all upon the sugar free agar. B. kill en sis 

 is also of interest; it is a degenerate culture of feeble pigmentation, 

 and still shows a lingering tendency to return to normal if oppor- 

 tunity affords, i. e., upon a fresh transfer from an old culture, or 

 upon transference to a new (here a sugar) medium. 



The five day growth presents the same differences, though less 

 distincfly. The mosaic appearance of B. ruber indicus and 

 B. rutilus is a beautiful expression of the existence of some pig- 

 ment-producing individuals among the mass of those not producing 

 pigment. This seems to argue that, here on solid media at least, 

 the presence of sugar has the effect not of modifying the pigment, 

 but of either permitting it unmodified or of inhibiting it. That the 

 acid formed from the sugar is the inhibiting influence may be ques- 

 tioned because of the early appearance of the differentiation. The 

 effect of acid directly upon the pigment may explain the more violet 

 red color of B. ruber miquel after five days, and the darker 

 color of B. a m y 1 o r u b e r. The 'late and luxuriant appearance of pig- 

 ment inB. ruberbalticuson sugar agar is a peculiar result entirely 

 inexplicable on the acid theory. It is to be noted that the three 

 cultures which produce early luxuriant pigment on sugar agar are 

 among those, of the whole series, which produce the most active fer- 

 mentation of sugars in the fermentation tube. 



It seemed possible to obtain some light upon the question of 

 growth-luxuriance and pigment-luxuriance by eliminating the bouillon 

 from the ordinary agar medium. Accordingly a series was grown 

 upon agar 1,5 %, peptone 1 | , and water. This medium was first 

 tried of different reactions, 1,5 | acid, neutral, and 1,5 | alkaline 

 to phenolphthalein. The same medium, neutral, was used with the 

 addition severally of 1 | pure dextrose, lactose, and saccharose. 

 Two differences between the "meat-free" medium and the ordinary 

 nutrient agar were noticeable, though hardly measurable. The growth 

 is more limited, i. e., less spreading and "massy", and the pigment 

 is in general more intense in the former. Some of this depends, without 

 doubt, upon the vigor of the culture, a particularly vigorous strain being 

 able to overcome slight differences in the media, expressed, in feeble 

 strains like B. kiliensis, by a series showing distinct gradation. 



(See Table IV p. 33.) 



This 48 hour table brings out several points : 



1) The tendency to violet red pigment on the more acid, to 

 orange red on the more alkaline media. 



2) The similarity of pigment color on dextrose and saccharose 

 agar to that on sugar free agar of acid reaction. That is, acid is 

 probably formed from assimilation of these two sugars. 



3) The similarity of pigment color on lactose agar to that formed 

 on sugar free neutral agar; i. e., lactose is probably not easily 

 assimilated. 



This and the last named point seem to afford evidence of the 

 activity of sucrase but not of lactase. 



