334 



B. prodigiosus likewise remains constant after repeated inoculations at 30 C., 

 whilst the control culture, without carbonate but for the rest under the same con- 

 ditions, strongly varies. The same result may be obtained with magnesiumhydro- 

 phosphate (Mg H POi . 2 HaO) to excess; this, however, quickly precipitates, 

 and in order to be active should be used in a bouillon-agarplate or in a thin 

 layer of liquid. In ordinary bouillon-agarplates i pCt. of this salt changes entirely 

 into crystals of ammoniummagnesiumphosphate (Mg NH4 POi . 6 HYO) the plate 

 becoming quite transparent; a plate with 3 to 4 pCt. on the other hand, 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 these the original form is found unchanged. As by 

 transplantations in rapid succession (and under constant and favourable conditions) 

 no change occurs during thousands of cell-partitions, this variability cannot repose 

 on some law governed by internal causes only, but a particular agency is wan- 

 ted, which may have its seat within the cells ; but which must yet be enacted on 

 by external circumstances. 



Although the variability can reveal itself already in an ordinary same well 

 arranged culture, e.g. in bouillon or in maltwort, allowed to stand for a few 

 weeks, yet this process may considerably be accelerated by repeated transplan- 

 tations, not after a very short time, but with longer intervals, for example two 

 days, with cultures kept at 33 C., a not too small quantity of the material for 

 the inoculation being used, e. g. two loops of the platinum thread. After three 

 or four repetitions, so after about a week, the variation can then be in full 

 course, the first culture, left to itself, not yet showing any perceptible change. 



This evidently reposes on the following circumstance. The influence which 

 causes the variability in the culture when it gets older, acts in the chosen con- 

 ditions already after two days. If now a re-inoculation is performed, the germs 

 affected by that influence can increase as well as those that remained normal, 

 whilst by not re-inoculating, thus in the first culture, the non-affected germs are 

 by far more numerous and remain so as the cell-division slackens after the second 

 day, because of want of food. At inoculation after two days there result at each 

 time new modified germs, and those which are modified already, are enabled to 

 augment without losing their modification. 



In this explanation it must further be accepted, that a transplantation after 



