904 
at all occurs. On the thiosulfate plates the germs preserve their 
autotrophy longer than ou the broth plates, but there too, this 
power finally gets lost. The real cause of this loss is not yet quite 
explained. With certainty it can only be said to take place when 
the concerned gerins augment when fed with organic food. 
Especially on the broth plates at 30° C. the colonies develop 
rapidly. It seems that four or five species are thereby active. Three. 
or four denitrify strongly in broth bouillon with 0.1 to 1 °/, potassium- 
nitrate, and they predominate so much that non-denitrifying species 
are not easily found. There is even no surer and easier method to 
obtain bacteria denitrifying with organie food than this anorganic 
denitrification, for although it is often difficult to isolate the active 
bacteria from the organic denitrifications, this is here by no means 
the case ’*). 
Among the colonies obtained from the anorganie mixture there 
are, as said, some which do not denitrify with organic food. 
Probably they live in the sulfur-chalk cultures as saprophytes at 
the expense of the organic matter formed by the autotrophes. 
On silicic-thiosulfate-nitrate-chalk plates develop, after two or three 
weeks, yellowish colonies of 1 to 14 mm. in diameter and nearly 
1 mm. high, evidently autotrophic. In the anorganic mixture, freed 
from air by boiling, they cause a vigorous denitrification after 24 
hours at 28° C. already. When sown on broth-gelatin the colonies 
appear to consist of two soft varieties?) of B. stutzeri, which do not 
melt the gelatin and of which one shows the usual structure; the 
other, the commonest by far, lacks that structure completely, 
nevertheless it resembles B. stutzeri in the other cultural aspects. It 
consists of a white soft mass of extremely small rodlets. In broth nitrate 
both show strong denitrification, especially the soft form, so that it 
is one of the most intensely denitrifying bacteria I know. At re- 
inoculation from the organic into the anorganie food we also find 
here that the autotrophy and the power of anorganic denitrification 
are lost. 
1) The most important denitrifying soil bacterium, the spore-forming Bacillus 
nitroxus, loses its denitrifying power quite or partly by growing on aérobic plates. 
Other species, such as Bacteriwm pyocyaneum, B. stutzeri, B. denitrofluorescens 
preserve, in aérobic plate cultures and in the collections, their denitrifying power 
unchanged for years. 
2) In reality there are three varieties, but the third which shows the character 
of the ordinary tough, folded colonies of B. stutzeri, is rarer. — It must be 
admitted that the difference between the soft colonies and the typical B. stutzeri 
is, superficially, considerable, and I think that many other observers would bring 
them to distinct species. 
