335 



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 magnifying 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 must be present, for from the seemingly homogeneous matter large 

 numbers of white and rose variants are 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 seem to prove that the frequent re- 

 petition 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. prodigiosus 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 quali- 

 tative 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 ). 



2. roseus i. 



3- ;> 2. 



') About 1890 from mouldering bones of a gelatinfactory near Delft. 



