905 
The principal species. 
The colonies from the sulfur-chalk denitrifications, which develop 
on the broth plates are for a part coloured yellow or reddish brown 
by earotin’), for the greater part, however, colourless. The brown 
species is a Micrococcus; it liquefies the gelatin and the micrococci 
differ much in size; the smaller ones are highly motile, but they 
lose their motility when transferred to broth-agar, whereby their 
denitrifying power, too, disappears. The yellow species is related to 
the brown and consists of small very motile rodlets. Here also the 
same variability. 
The uncoloured colonies are of two types: soft, and tough or slimy. 
All the soft ones-liquefy the gelatin on which they grow intensely ; 
sugars are not fermented, no fluorescence; they belong to three 
classes different by their size: 1. Extensive, rapidly growing, strongly 
denitrifying. 2. Middle sized, less rapidly growing, as strongly deni- 
trifying. These two classes are allied by intermediate forms and 
may be brought to one single species, Bacterium denitrificans. 
3. Very small and feebly growing, non-denitrifying bacteria, manifestly 
living at the expense of organic food produced by the other species 
through chemosynthesis. 
With the pure cultures on an organic medium of the second form, 
I have succeeded in obtaining very feeble anorganic denitrifications, 
hence, chemosynthesis. This could, however, only be observed in the 
quite young cultures that had but for a short time grown on the 
broth medium. Cultures which have longer than two or three days 
been in contact with organic food and the air, can no more denitrify 
with sulfur and chalk, but still very well in saltpetre broth. For 
demonstrating the anorganic denitrification, test tubes are partly filled 
with mud, previously deprived of organic matter by keeping the mud 
under a saltpetre solution. To the mud sulfur and chalk are added and 
subsequently 1°/, saltpetre; the dissolved oxygen and the germs are 
removed by boiling; sterilisation is not wanted, as spore-formers 
with chemosynthesis do not exist. 
Entrance of air is prevented by a hollow glass sphere, well fitting 
in the tube and floating on the liquid, but this precaution is not necessary. 
With the pure cultures of the soft colonies I could not obtain 
any evolution of gas in this mixture, they manifestly lose their 
autotrophy still sooner than those of the second group. 
The more or less tough, or slimy, or cartilaginous colonies belong 
h This pigment is soluble in CS, and turns blue or violet with concentrated 
sulfuric acid. 
