— 
Vol.58.] | CONCRETIONS IN THE LOWER COAL-MEASURES. OF 
sulphuretted hydrogen and decayed organic matter. The animal 
matter and a large part of the vegetable matter had disappeared. 
Upon the surface of the fluid was a clotted gelatinous mass of 
fungi and bacteria in which were disseminated very fine spheres 
of calcium-carbonate, and also some of the harder vegetable tissue 
thoroughly impregnated or fossilized by the same mineral. The 
black material was ferrous sulphide. 
This experiment has been repeated several times by me, and IL 
have found that the action could be started almost immediately by 
introducing a small quantity of sewage which contains the reducing 
or anaérobic bacteria in large numbers. The blackening was then 
noticed after the first three davs, and after a few weeks all the 
softer vegetable tissues were dissolved out, leaving the harder parts 
often with adhering nodules of carbonate of lime. (See fig. 5, 
p. 96, showing scalariform cells of carrot with nodules upon them.) 
Many spheres and modified crystals were also found embedded in 
the bacterial jelly (fig. 6, p. 56): these show that the centre of 
activity is in this jelly, and their rounded form is a direct result 
of the medium in which they have been formed, the bacterial jelly 
behaving in a similar way to gum, glue, and other colloids. 
The solutions tested contained little or no calcium-sulphate after 
this action: hence all the calcium-sulphate is converted into caleium- 
carbonate if the conditions are favourable. 
When sewage was introduced into a nutrient medium containing 
calcium-sulphate and ferric hydrate, but without solid vegetable or 
animal matter, the same result was obtained, the whole mass 
becoming black, owing to the formation of sulphide of iron, in a 
few days. But if, after such introduction of sewage, the material 
was sterilized by heat no blackening ever took place, and this was 
sufficient to show that the changes described above were due entirely 
to bacteria. 
J have made several endeavours to cultivate these reducing 
organisms upon ordinary solid media such as sugar, but so far 
without success, and it has therefore not been possible to isolate 
and further examine them. 
The reactions brought about by these anaérobic organisms are 
represented by the following equations : — 
(1) CaSo,+2C=2C0,+Cas. 
(2) CaS+C0,+H,O=CaCO, +H,8. 
(3) Fe,(HO),+3 H,S=2 FeS+6H,0+48. 
Many minor reactions, however, appear to take place. In one 
experiment a iarge quantity of crystalline sulphur was found on 
the stopper of the bottle where limited oxidation could take place. 
This may have been produced as shown in the following equation : 
H,S+O=H,O+S8. 
The deposit also contains sulphur, and sometimes radiating needles 
very like calcium-oxalate. 
