( 640 ) 
that “dextran” is a modification of cellulose, and the till noW not, 
explained secondary changes, observed in so many eel l-w alls, may 
then freely be ascribed to the action of specific enzymes, related to 
the viscosaccharase. 
Why the emulsion is distinctly observed in agar, and less easily 
in gelatin-plates, must probably be explained by the dimension of 
the molecules of viscosaccharase, which are small enough to enter 
without much trouble the relatively wide canals of the agar, but 
too large to pass through the much narrower ones of the gelatin. 
Many of the experiments here related I owe to Mr. D. C. J. 
Minkman, assistant in my Laboratory. 
EXPLANATION OF THE PLATE. 
Fig. 1. Colony of Bacillus mesentericus vulgatus on: canal water, 2% of agar, 
l°/ 0 of cane-sugar, 0.02% KN0 3 and 0.02% KaHPO^ with emulsion around 
colony. Magnified 8 times. 
Fig 2. Colony of Bacillus emulsionis n. sp., on canal water, 2% of agar, 0.1% 
of cane-sugar, 0.02% GINH 4 , 0.02% K 3 HP0 4 , with emulsion around colony, 
Magnified 9 times. 
Microbiology. — “ Variability in Bacillus prodigiosus” By Prof. 
M. W. Beijerinck. 
In a former paper 1 ) I showed how easily new constant variants 
of Bacillus prodigiosus and other microbes may be obtained. Here 
follow some further observations, made with the aid of Mr. H. C. 
Jacobsen, assistant in my Laboratory. 
The keeping constant of the cultures. 
The principle on which the keeping constant of B. prodigiosus 
seems to repose is preventing the cultures from becoming alkaline by 
their own action. . Thus, by re-inoculating in quick succession, for 
instance every 24 hours, into bouillon or on bouillon-agar at 30° C., 
each form of Bacillus prodigiosus, whether the natural or normal 
form, or a variant obtained from it, remains unchanged probably 
for an indefinite time. 
For the transplantations only very little material must be used 
and an abundance of food. 
If some lactic acid is added, for instance 0,5 to 1.5 cm 3 normal 
per 100 cm 3 ot bouillon, the culture likewise remains unchanged 
l ) Royal Acad, of Sciences 21 Nov. 1900, 
