193 



Then a moment follows in which the colour of the added potassium- 

 permanganate disappears onlj slowly: this is the oxidation of the 

 organic matter, extracted by the diluted sulphuric acid, for in a 

 drop of this extract, placed on a piece of (ilter|)aper soaked with 

 potassium ferroeyanid no feno can be demonstrated any more. 



The sand samples ai-e most often not so rich in organic compounds 

 as the clay-samples, which often contain peat. Presumably this 

 generates a strongei- sulphate-reduction than is possible in the sand- 

 samples, and this is probably the reason why clay can be darker 

 in colour than sand. 



Van Dki>den ^) has shown that for sulphate-reduction organic bodies 

 are required which are easily oxidizable. This justifies the assumption 

 that in the organic substances, demonstiated by us, there are some 

 bodies difficult of oxidation and others again which are easily oxidi- 

 zable, which is proved indirectly by the sulphate-reduction that 

 manifests itself in the sand-, clay-, and peat-samples. 



Also the 3"^ condition, the pi-esence of the required mineral 

 compounds, was satisfied. In our examination for sulphate only small 

 amounts could be demonstrated, wdiich is explained by the disappearance 

 of sulphate through sulphate-reduction. 



One of the mineral combinations is that of the insoluble, black- 

 coloured ferric siilphid, formed by the iron and the libeiated hydrogen 

 sulphid, as pointed out already in § 3. 



From the foregoing we may deduce that the conditions of 

 anaerobic life which we found in the deeper layers of the soil, 

 fairly agree with the prevailing sulphate-reduction. 



§ 5. The content of ,,aerohic" and ,,anaerobic" yerms of the 

 deeper layers of the soil. 



Besides the demonstration of sulphate-reducing spirilla in the soil- 

 samples, another question arises, viz. whether they contain other 

 germs and whether these belong to the aerobes or the anaerobes. We 

 examined the samples: 



B 28 29.00 M — A. P. (clay with peat) 



B 29 6.50—10.50 M — A.P. (clay). 



B 31 25.30 M— A.P. (peat). 



The number of germs w^as ascertained in the way described in 

 § 3. With a sterilized spatula inoculation-material was taken from 

 the soil-samples, it was then shaken up in sterile tapwater and 



1) Centralbl. f. Bakl. Bd. XI, 2te Abt. 1903, p. 83. 



