DEGRADATION OF THE ALBUMINOIDS. 293 



depends, however, not solely on the species of ferment, but also 

 on the composition of the nutrient medium, a circumstance which 

 explains the contradictory results obtained by different workers. 

 Thus, for example, STAGNITTA-BALISTRERI (I.) denied that Bacillus 

 SubtiliSj Bacillus tetragenus, the so-called Wurzel bacillus, and others, 

 could form sulphuretted hydrogen ; but PETRI and MAASSEN (III.) 

 then showed this contention to be incorrect, and that, in presence 

 of peptone, the gas in question is produced by these microbes. In 

 other cases, again, this product may be masked, e.g. by combina- 

 tion with ammonia formed at the same time. A good deal of the 

 sulphur present in the nutrient medium is utilised by the bacteria 

 themselves for structural purposes, the amount so consumed having 

 been found by M. RUBNER (!) to be equivalent to 23-40 per cent, 

 of the total sulphur in the medium. The sulphur in organic com- 

 bination is first occluded, a circumstance harmonising with the 

 well-known fact that the sulphur in albuminoids is very easily 

 removed. The more delicate processes leading finally to the 

 evolution of sulphuretted hydrogen, still remain unelucidated. 

 PETRI and MAASSEN (IV.) are of opinion that the bacteria liberate 

 hydrogen, which in the nascent state then extracts sulphur from 

 the sulphur compounds and combines with it. They found that 

 very little of the gas in question is produced when nitrates are 

 present in the medium, but that these latter are thereby reduced to 

 nitrites. With reference to the fact (put forward to refute this 

 explanation) that sulphuretted hydrogen is liberated by aerobic 

 bacteria in well "roused" (aerated) cultures, Petri and Maassen 

 showed that hydrogen is also liberated under this treatment, and 

 that consequently the presence of air favours the reducing action. 



The faculty of producing sulphuretted hydrogen is very common 

 among the pathogenic bacteria, being absent in not a single one 

 out of thirty-seven species examined ; and in many of them e.g. 

 the bacilli of swine erysipelas the inoculated nutrient solution 

 fairly bubbles, from the quantity of gas liberated. A convenient 

 means of detecting and separating sulphuretted-hydrogen-generating 

 microbes from a mixture of bacteria by the aid of plate cultures is 

 afforded by the ferro-gelatin, recommended by A. FROMME (I.) for 

 this purpose ; i.e. a peptonised meat-juice gelatin qualified by 3 

 per cent, of iron saccharate or tartrate. In such nutrient media 

 each colony of the sulphuretted hydrogen bacteria will become 

 surrounded by a black halo of FeS. 



The conversion of sulphates into sulphides by bacterial agency 

 is also a decisive indication of reducing power. The conditions of 

 vitality of a particularly active species of fission fungus were in- 

 vestigated by BEYERINCK (II.), who named the organism Spirillum 

 desulfuricans. This strictly anaerobic microbe is utilised in practice 

 in so far that by skilfully encouraging its development pit-water 

 very rich in gypsum has been entirely freed from sulphates (CaS0 4 

 being converted into CaS and FeS) and rendered suitable for 



