848 
The Micro-crrjcmisms of the Soil. 
oxygen, according to the generally accepted theories, depended upon 
light and chloroi^hyll ; consequently the produced oxidation could 
only occur on the extreme outer surface. An exception to this 
heretofore unrestricted rule has been found by Engelmann, as 
well as one by Heraus. According to Engelmann, Bacterium 
2 ')hotometric'um sharply discriminates between lights of different 
intensity and wave lengths. The influence of light upon the bacteria 
is directly proportionate to the intensity. When the intensity is 
suddenly decreased, the bacteria shoot backwards with opposite 
rotation (the author calling this a terror motion), consequently a 
well-defined illuminated spot in an otherwise dark drop serves as a 
trap for these bacteria. They cannot leave, since the terror motion 
causes them to move back into the illuminated field as soon as they 
come to the dark outline. 
The mobile forms principally congregate in the ultra-red rays of 
solar light, i.e. physiologically in darkness, and in them — as in the 
visible parts of the spectrum — in places closely corresponding to what 
are known to physicists as the absorption bands of bacterio-purpurin. 
This constant ratio between absorption and photo-kinetic action 
clearly indicates that the prime effect of light is equivalent to the 
carbon-dioxide dissociating processes of plants containing chlorophyll. 
The bacterio-purpurin is a true chromophyll, inasmuch as it 
converts the actually absorbed energy of light into potential chemical 
energy. When lights of different colour were employed, the evolu- 
tion of oxygen increased with the absorption of light by the purple 
bacteria. This .shows that the power of developing oxygen is not the 
specific property of a certain colouring matter, as the organisms 
contain no chlorophyll. 
It is not surprising, therefore, that other organisms, either 
coloured or uncoloured, are found to possess the property of assimi- 
lating carbon in the absence of light, and evolving oxygen. Such a 
discovery has now been made — Hueppe substantiating a communi- 
cation from Heraus that certain colourless bacteria produce fi’om 
humus and carbonates, in the absence of light, a body closely resem- 
bling cellulose. Oxygen is liberated, but remains unobserved, as it is 
immediately used to convert the ammonia by oxidation into nitric acid. 
The next question is : To what extent do the oxidising organisms 
partake in the oxidation phenomena actually occurring in the 
soil ? According to E. W ollny the oxidation of cai’bon dioxide is 
almost completely to be attributed to the activity of small oi’ganisms, 
of which Adametz estimated that there are about 500,000 to 1 
gramme ( = 15.\ grains) of soil. As in all such expeiiments, this con- 
clusion is based upon the fact that no evolution of carbon dioxide 
takes place, or if it does occur it is forced to a minimum, in a sterilised 
soil under otherwise favourable conditions. 
Liberation op Combined Nitrogen. 
Tliis may take place during putrefaction under the greatest 
possible exclusion of oxygen, or during decay in the presence of 
