138 ATLAS OF BACTERIOLOGY. 



4. Sulphuretted Hydrogen. 



Sulphuretted hydrogen is a very widely distributed 

 bacterial product. It is easily demonstrated by 

 fastening, by means of the cotton plug, a moist strip 

 of lead acetate paper in the neck of the culture tube 

 and closing it with a rubber cap (made of black rubber 

 free from sulphur). Frequent observations of the 

 originally brownish, later black, often very feeble dis- 

 coloration of the paper is necessary, because some- 

 times the color fades away at a later period. Tests 

 which are apparently negative should not be ter- 

 minated too soon. The literature consists mainly of 

 articles by Petri and Maassen (A. G. A., VIII., 318 

 and 490), Eubner, Stagnitta-Balistreri, and Niemann 

 (A. H., XVI.). 



Sulphuretted hydrogen may be formed from : 



1. Albuminoid bodies. (It is well known that 

 mere boiling eliminates H 2 S from egg albumin). 

 According to Petri and Maassen this power inheres 

 in all the bacteria examined upon a fluid nutrient 

 medium which is rich in peptone (five to ten per 

 cent) and free from sugar; in bouillon free from 

 peptone very few varieties form H 2 S (for example, 

 bacterium vulgare); in bouillon containing one per 

 cent peptone, about fifty per cent of the bacteria 

 (Stagnitta-Balistreri) . 



2. Powdered sulphur. In nutrient media to which 

 pure powdered sulphur has been added all bacteria 

 produce much larger amounts of sulphuretted hy- 

 drogen than without this addition. Petri and Maas- 

 sen regard this production of sulphuretted hydrogen 



