( 641 ) 
after a prolonged series of transports, if these are always carried 
out before the acid is neutralised by the alkali produced from the 
bouillon by the bacteria themselves 1 ). 
Addition of 1 to 2 pCt. of glucose acts in the same manner as 
free acid, B. prodigiosus therefrom producing acid which may rise, 
if sufficient glucose is added, to 3 to 4 cm* normal per 100 cm 5 
of bouillon. As the titre of alkali, originating in the bouillon alone, 
can amount to 2.5 cm* N per 100 cm* of bouillon, and as from 
1 pCt. of glucose there results no more than 1.5 to 2 cm* N of 
acid, addition of 1 pCt. of glucose is sufficient to prevent variation, 
if the re-inoculations take place quickly; but not if effected with 
long intervals, for in the latter case more alkali may result from 
the bouillon than acid from the glucose. 
If to the bouillon so much ammoniumcarbonate or natriumcarbonate 
is added that the titre of alkali amounts to about 3 cm* N per 100 
cm* of the medium, B. prodigiosus likewise remains constant after 
repeated inoculations at 30° C., whilst the control culture, without 
carbonate but for the rest under the same conditions, strongly varies. 
The same result may be obtained with magnesiumhydrophosphate 
(Mg H P0 4 .2 H 2 0) to excess; this, however, quickly precipitates, 
and in order to be active should be used in a bouillon-agar plate or 
in a thin layer of liquid. In ordinary bouillon-agarplates 1 pCt. of 
this salt changes entirely into crystals of ammoniummagnesiumphos- 
phate (Mg NH 4 P0 4 .6 H a O) the plate becoming quite transparent; a 
plate with 3 to 4 pCt. on the other band, remains white and turbid. 
Although it may be admitted that by these various means the 
formation of secretion products by the bacteria is prevented, on 
whose stimulating action the variability probably reposes, yet it, is 
not clear how this preventing takes place. Evidently substances 
should be thought of here which, once produced, cannot or only 
with difficulty leave the bacterial body. 
Of the said means quick transplantation is the simplest for always 
disposing of constant stocks for the experiments. 
The origin of the variants in general. 
When cultures, placed under favourable nutritive conditions, but 
for the rest prepared without special precautions, are growing older 
between 10° and 30° C., they exhibit a certain variability at which, 
as formerly described (1. c.), variants are thrown off, while beside 
!) At 4 cm 5 of acid per 100 cm 3 of culture liquid the growth of B. prodigiosus 
is slacfceped, at 9 cm 3 it is quite stopped. 
