PHYSIOLOGY OF THE IRON BACTERIA 277 



Consequently, these organisms may develop into an- actual nuisance to water- 

 technicists by penetrating into the clarifying reservoirs and delivery pipes, and 

 there growing so vigorously as to completely obstruct the passage of the water, 

 and thus interrupt the service of distribution. Many towns deriving their 

 water-supply from a soil or river water rich in iron have suffered from this 

 nuisance ; Lille, for example, as reported by GIARD (III.), and Berlin, as 

 mentioned by W. Zopf in his ( treatise already referred to. In the waterworks 

 at Lake Tegel, from which the greater part of Berlin derives its supply, these 

 bacteria (and especially the " well-pest," Crenothrix polyspora) flourished so 

 luxuriantly that they constituted more than one-half of the layer of sediment 

 (about forty inches in depth) gradually collecting at the bottom of the reservoirs. 

 One means of obviating this nuisance (although not practicable on a small scale) 

 is by freeing the water from its content of ferrous oxide, for which purpose 

 P. WOLTERING and A. SASSEN (I.) recommended a method (which is said to 

 answer) consisting in passing the water through coke towers where the ferrous 

 oxide is converted into ferric oxide, the latter being then removed by suitable 

 strainers. 



Finally, Cladothrix odorifera merits brief consideration. Every one is 

 acquainted with the peculiar smell of the soil, more particularly when moist, 

 e.g. after a brief shower of rain. According to the researches M. BERTHELOT 

 and G. ANDRE (I.), this odour is due to a neutral organic compound, present in 

 the soil and volatilising at the same time as water vapour. The producer of 

 this (not yet precisely identified) compound has now been recognised by RULLMANN 

 (I.) in a new species of bacterium, viz., Cladothrix odorifera. It occurs along 

 with Cl. dichotoma in the soil, and, like the latter organism, can be cultivated 

 on nutrient gelatin ; but whereas the colonies of Cl. dichotoma are inodorous, 

 liquefactive, and turn the substratum brown in a short time (two days), those 

 of CL odorifera, on the other hand, retain their chalky white appearance and 

 evolve the aforesaid earthy smell. RULLMANN (II.) also found that this species 

 is capable of withstanding the influence of drought and poisons, being able to 

 bear exposure for twenty-four hours to a i : 1000 solution of corrosive sublimate. 

 Like its aforesaid congener, Cl. odorifera possesses considerable oxidising power, 

 though this is manifested by the transformation of ammonia into nitric acid, 

 and not by the conversion of ferrous into ferric oxide. This mode of action 

 is not peculiar to this organism alone, but is shared in a still higher degree by 

 a group of bacteria whose acquaintance we shall make in chapter xxxvi. 



The iron bacteria are not the only Schizomycetes capable of liberating the 

 energy necessary for the maintenance of their existence from inorganic bodies. 

 In the next two chapters we shall make the acquaintance of fresh natural groups 

 and other processes similar to those described ; thus justifying the title of this 

 concluding section. 



