PHYSIOLOGY OF THE IRON BACTERIA. 361 



materials, an addition of, e.g. a few thousandths of i per cent, 

 of sodium acetate to ferruginous water being entirely sufficient to 

 bring them to a state of perfect development. This inexigency is 

 also indicated by the observation, made by 0. ROSSLER (I.), that 

 Cladothrix polyspora can be grown on bricks moistened with a 

 little ferrous sulphate solution. In 1894 M. BtfSGEN (I.) succeeded 

 in obtaining pure cultures of Cladothrix dichotoma on gelatin. 



The decomposing power of these organisms is very great, the 

 amount of ferrous oxide oxidised by the cells being a high multiple 

 of their own weight. This high chemical energy on the one hand,, 

 and the inexacting demands in the shape of food on the other, 

 secure to these bacteria an important part in the economy of 

 Nature; the enormous deposits of ferruginous ochre and bog- 

 iron ore, and probably certain manganese ores as well, being the 

 result of the activity of the iron bacteria. 



Moreover, they make their presence evident not only in natural 

 water basins, but in all other places where water rich in iron is to 

 be found in quantity. 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 only practicable on a small scale) is by freeing the water 

 from its content of ferrous oxide, for which purpose P. WOLTERTNG 

 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 particu- 

 larly when moist, e.g. after a brief shower of rain. According to 

 the researches of M. BERTHELOT and G. ANDRE" (I.), this odour is 

 due to a neutral organic compound, present in the soil and volati- 

 lising 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, lique- 



