( 642 ) 
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 wanted, 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 transplantations, not after a very short time, but 
with longer intervals, for example two days, with cultures kept at 
30° 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 conditions 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 rednoeulating, 
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 transplan¬ 
tation after two days gives no cause for atavism; for if this were 
the case, the reverse ought to take place of what is observed: 
after a week’s growth the first culture should be more varied than 
that which has repeatedly been transplanted, but this is not so. This 
shows how carefully the variation experiments must be carried out 
in order not to become obscure. 
Particularly the cultures on solid media must very accurately be 
observed. If these are allowed to stand' for some days or weeks 
without further precautions, then in many cases, even with magni¬ 
fying glass or microscope no variation at all can be detected, although 
it is actually going on, commonly to “rose” or “white”. 
Colony culture then shows that here and there varied germs or 
groups of such germs mnst be present, for from the seemingly 
homogeneous matter large numbers of white and rose variants are 
