( 643 ) 
obtained, which prove as constant as the normal form itself. However 
unchanged colonies, representing the pure stock and producing a 
material as. fit for further experiments as the original culture, lie 
among the variants. 
Experiences afforded by other bacteria seein to prove* that the 
frequent repetition of the thus possible process of selection, produces 
a form which varies less than the original material. But it is not. 
here the place to enter upon this important fact. 
All colony cultures of B. prodig iosus are best made on bouillon- 
agar-plates, which after solidifying have been cautiously dried on a 
thermostat at circa 40° C. The water which then condenses on the 
glass cover can easily be removed; if this is neglected, B. prodigiosus, 
which is strongly motile, spreads over the surface of the agar and 
the colonies coalesce. 
I shall now enter into a short discussion of the most important 
variants. 
The obtained variants. 
The variants derived from B. prodigiosus may be considered as 
plus- or gain-variants, minus- or loss-variants, and qualitative variants. 
This is exposed below in the table of descent, which shows the 
origin of the obtained forms; the qualitative variants (auratus and 
hyalinus) are placed on the same line with , the normal form, the 
plus-variants above it, the minus-variants beneath. Hence, the arrows 
not only denote the descent but also whether the variability reposes 
on gain or loss of characters, or if it is qualitative. Dotted arrows 
indicate that atavism has with certainty been observed. The names 
indicate the chief qualities characterising the variants. 
A survey of the variants without regard to their descent precedes; 
then follows their pedigree, which does not repose on hypothesis, 
but simply gives the result of the experiments. 
The obtained variants are : 
1. Bacillus prodigiosus. Normal form, isolated from nature 1 ). 
roseus 1. 
„ 2 . 
albus. 
„ hyalinus . 
viscosus. 
„ albus . 
auratus. 
*) About 1890 from mouldering bones of a gelatinfactory near 
Proceedings Royal Acad. Amsterdam. Vol. XII. 
Delft. 
43 
