339 



perature, at which rapid growth and vigorous melting occur. By daily streaking 

 off on a bouillon agarplate the same colony obtained on such pure gelatin, and 

 provided the temperature be kept between 14 and 17 C., we find, on the fifth 

 or sixth day, the first rose variants, either or not with the white, which under 

 these conditions appear later. Two rose variants (table N. 2 and 3) are easily 

 distinguished, but it is possible that there are many more whose perception is 

 beyond the reach of our observation. In any case, it is a fact that the character: 

 the faculty of producing pigment*, is divisible in many ways. The hereditary 

 constancy of at least one of these rose variants proved not to differ from that 

 of the normal form. 



Another method to obtain rose variants is cultivation of the normal form 

 in bouillon, which by evaporation has been reduced to a threefold concentration. 

 After a single transport already, a large number of rose variants (3) had appeared 

 by the side of normal forms; by a much lighter colour they showed a disposition 

 to lose their colour entirely. The variability of the different rose variants is not 

 the same; the form, obtained by the concentration experiment (3) produces, more 

 readily than the rose variant (2), as well red normal forms (i) as white ones (4). 

 For the rest, this more variable variant has also proved to remain constant when 

 quickly transplanted. 



Cases of atavism are frequently observed in these experiments. Thus, for 

 example, the production of the normal form from viscosus (6) may easily be seen 

 if the latter grows for a fortnight without transport on a bouillon-agarplate ; along 

 the margin of the streaks some few normal colonies (i) will then become per- 

 ceptible. 



The ff//>#s-variants, also have a disposition to throw off a few red normal 

 forms, but they do so only after growing for weeks or months on bouillon-agar; 

 at first they are very constant. 



The to a certain extent completely regular production of the same variants 

 of Bacillus prodigiosus, suggests the existence of variability in a special and deter- 

 mined direction, of orthogenesis, as Eimer expressed it. 



As under different nutritive conditions the same variant may appear, the 

 food itself cannot be the stimulus; there must be, as said above, another cause 

 in the interior of the cells, which, for B. prodigiosus, seems only active in an 

 alkaline environment. 



On the other hand, the food, in a wider sense, has certainly a decisive 

 influence on the variability, albeit indirectly. So we considered already the in- 

 fluence of the alkaline reaction of the medium if this alkali is produced by the 

 microbes themselves. Another example is the following. As well in malt-wort as 

 in bouillon the viscosus variant is regularly produced; but from malt-wort the 

 auratus variant, which so readily takes rise in bouillon, is not obtained at all. 

 Indeed, every culture condition gives a peculiar but constantly returning mixture 

 of variants, differing both quantitatively and qualitatively from that found under 

 any other conditions. But the real factors here active could not as yet be detected. 



From the foregoing the following results may be derived, 

 i. Bacillus prodigiosus produces as well qualitative, as gain- and loss-variants, 



22* 



