( 636 ) 
be distinguished with a magnifying glass. At feeble magnification 3 
they ; might be taken for droplets of oil suspended in the agar, but 
as strong sulphuric acid dissolves these drops immediately, and a 
feebler acid more slowly, there can be no question of oil or fat. 
Characteristic for the reaction is that it can only be distinctly ^ 
observed in agar but imperfectly in gelatin. In the agar the 
process is impeded when acid is produced by the microbes. Thus 
bouillon-agar, yeastwater-agar, and wort-agar with cane-sugar can' % 
well be used, but the emulsion is more distinctly formed in S 
agar with mixtures of substances that prevent the acidification, ! 
to which cane-sugar is so very apt. For that reason nitrates as 
nitrogen-food are especially favourable, as the withdrawing of nitrogen 
then necessarily must produce an alkali, while for example ammonium- i 
salts, used as source of nitrogen, must promote the acid reaction. - 
A good experiment to produce the emulsion is the following: A plate 
is prepared of the composition: tap water, 2 °/ 0 of agar, 2 °/ 0 of cane- 
sugar, 0,02 °/u KNO, and 0,02 % K,HP0 4 . Nitrogen food may also 
be quite left out, so agar-plates with 10 % of cane-sugar and bikaliura- 
phosphate only, are very well fit to demonstrate the emulsion with 
Azotobacter and the hereafter mentioned Bacillus emulsionis. The 
quantity of cane-sugar can vary between 0.1 % and 50 % without 
much difference in the result. 
After the solidifying of the agar-plate and the removal of the 
adhering water, soil-bacilli are dispersed, obtained by shaking some 
garden-soil with water, and heating it a few minutes at 70° to 80° C. 
in order to kill the not sporulafing microbes. Then the water is 
poured over the plate hnd allowed to flow off. The adhering germs, 
for so far they live, are nothing but spores of bacilli, which can 
germinate at 30° C. 
After one or two days the colonies become visible and simulta¬ 
neously the emulsion around some of them ; the majority does not 
produce the emulsion. 
Cane-sugar may be replaced by raffinose, which acts in the same 
way; but glucose, levulose, mannose, galactose, lactose, maltose, 
trehalose, melibiose, mannite, inulin, dextrin and xylose, do not give 
the emulsion. 
The emnlsion is distinct round, the colonies of Bacillus mesenterial* 
vulgatus (see plate Fig. 1), B. megatherium and a not yet described 
soil-bacillus, commonly also found in cane-sugar itself, recognisable 
by its small terminal spores, whiclr may be called Bacillus emul- 
sumu and whose transparent cotony is likewise given on the plate 
(Fig. 2). The emulsion is wanting in B. mb tills, B. mycoides, B. 
