190 



§ 3. The examination of the sand- and clay-samples for 

 sulphate-reduction. 



From a cheinioo-biologieal point of view it is interesting to 

 ascertain the origin of the ferric snlpiiid, whicli gives a dnll-gi-ev, 

 greyish bine to bluish-black colour to the soil-samples. The obvious 

 hj'pothesis that the ferric sulphid was formed by sulphate-reduction, 

 was in every respect substantiated by (he examination of the many 

 sand-, and clay-samples procured by means of the "puis". Thus the 

 sulphate reduction in the deeper layers of the earth underneath the 

 dunes appeared to be a bacteriological process of common occurrence. 

 The demonstration of sulphate reducing spirilla was performed 

 after the accumulation-method of Beijerinck, the culture-medium ') 

 used being: 



Tap water 100 



Na-lactate 0.5 



x^sparagin 0.1 



MgSO, . 7 aq 0.05 (or gypsum) 



FeSO, . 7 aq 0.001 



with which sterile stoppered bottles of ± 150 cc. capacity were 

 filled after infection with a quantity of the sand-, or clay-samples 

 under examination. They were filled up to the neck, then cautiously 

 stoppered and placed under 25° C 



BEiJimiNCK') showed that in this anaerobic procedure Microspira 

 desulfuricans is exclusively the causative agent of the sulphate- 

 reduction manifesting itself, as appears from the formation of hydro- 

 gen sulphid and the black fei-ric sulphid. 



My culture bottles showed in every respect the same progress 

 of the reduction process, so that hereby the exan)ined sand-, and 

 clay-samples gave evidence of the presence of Microspira desulfuricans. 

 The material used for infection of the medium was drawn from 

 the inner portion of the sand-mass in the "puis" by means of a 

 sterile spatula, and deposited in sterile wide-mouthed stoi)pered 

 bottles. Directly when the samples were received at the laboratory 

 they wei-e subjected to investigation. 



Sterile sampling could be effected to perfection only in clay-, and 

 peat-samples. This was performed aflei' Beuf^rinck's ') method. The 

 sample was split in two. From the fracture laid bare, the required 



1) A. VAN Delden. Beitrage z. Kenntn. d. Sulfaatreduktion durch Bakt. Gentralbl. 

 f. Bakt. 2e Abt. 1903. Bd. XI, p. 83. 



Ï) Verzamelde Geschriften. (Collected Papers) Vol. 4, p. 53. 



8) Verzamelde Gescliriften. (Collected Papers) Vol. 2, p 354. Note 2. 



