€ 1071 ) 
lacking in closely allied forms which are themselves constant and 
differ only in this quality. 
Another character by which the natural varieties of P. aromatica 
ave mutually distinct, consists in their very unequal power of lique- 
fying gelatin, this power being intense in some and quite absent in 
other varieties, with all intermediate degrees. The same is to be 
observed in the quercite bacteria; hence the variability of this property 
is in some degree a property of the whole group. 
All varieties, apparently without exception, produce in glucose 
bouillon about 3 em.” N acid per 100 em.” liquid. For growth, 
oxidation and acid formation, peptones are wanted as source of 
nitrogen, ammonium salts and nitrates can hardly serve as such and 
only in pure cultures, but by no means in free competition with 
other microbes. 
Although aromatic milk contains a great many quercite bacteria, 
its flora chiefly consists of other varieties of P. aromatica, but the 
following experiment, based on the principle: slow rising of the 
concentration of a good nutrient medium apt to produce a slight 
acidification, makes it possible almost exclusively to obtain the quercite 
bacteria. 
Large glass beakers are filled with 1 L. of distilled water and 
therein are floated a few small dialysators of parchment paper, 
manufactured by SCHLEICHER and ScHürr, of the shape of experiment 
tubes, each filled with about 15 em.” of extract of greenmalt. 
This extract is prepared by rubbing two parts of greenmalt with 
turee parts of water in a mortar and filtrating after some hours’, 
digeration at room temperature. The clear solution contains relatively 
little maltose and is of course extremely fit for bacterial growth, 
where, likewise as in milk, lactic acid ferments are able to develop, 
but only little lactic acid can be formed on account of the low rate 
of sugar. Kept in a room where the temperature varied from 15° 
to 20°C. the spontaneously corrupted infusions in the beakers produced 
at repeated experiments, made in December 1910 and January 1911, 
so great an excess of quercite bacteria, that other species could hardly 
be found in the black mass, obtained by streak inoculations on broth- 
agar quercite plates. 
If instead of submitting the malt extract to dialysis, different 
quantities of the extract itself were directly added to the water, 
then, with for the rest like conditions, much less quereite bacteria 
developed. 
The aroma formed in the malt extract is of the same nature as 
that found in aromatic milk. 
70* 
