1900] CHROMOGENIC BACTERIA 391 
gelatin containing glucose, lactose, etc., are examined. It will 
be seen that the main band has suffered displacement toward the 
tight, just as if an acid had acted slightly upon the coloring 
matter. Addition of acetic acid with the production of a purple- 
red color furnishes an absorption spectrum like that shown in 
fig. 14 (compare this with figs. 4,5,9). Mig. 15 is obtained 
when the violet solutions shown in fig. 73 are treated with an 
excess of fixed alkali (in this case sodium hydroxid), and the 
mixture shaken with air until blue (compare with jig. 8). 
The absorption curves represented on the plates are drawn 
to the scale of wave-lengths. The intensities are, of course, 
arbitrary, and are based upon a value which would permit of 
‘fepresenting a spectrum such as that of jig. Zo. Owing to the 
difficulty of judging the intensities of most ‘of the solutions 
examined, particularly after long intervals of time, it is probable 
that the curves may not be perfectly accurate as to intensity. 
The positions of the bands, however, are correct within the limit 
of experimental error. The results given are averages from 
examinations of many cultures extending over a period of more 
than two years. 
Most of the measurements have been made with a Kriss 
Universal Spektralapparat. It is, perhaps, needless to add that 
the usual precautions as to calibration, checking adjustments, 
_ tte., were observed. 
Growth on agar-agar.— On nutrient agar prepared as usual 
7 and rendered slightly alkaline with sodium hydroxid, a more or 
| [ess bluish-violet color is produced which diffuses through the 
Upper part of the culture, but is reduced where the air cannot 
penetrate. In this case the reduction of the coloring matter has 
been proved by experiment to be largely due to the action of the 
Culture medium, and not to products formed by the bacillus. In 
Young cultures the bluish tint is the strongest, in old ones the 
Ted tint. 
e blue 
If to the nutrient agar glucose or lactose is added, ae me 
| 'Svery marked, but soon becomes violet, then purple. 2 
= Of media inoculated by streak the change from blue to 
