276 THE IRON BACTERIA 



occur in particular abundance in such waters as are rich in iron, not in the form 

 of oxide, but as the soluble bicarbonate of the protoxide, FeH,(C0 3 ),. Ferrugin- 

 ous springs, ascending from the deeper strata of the rocks, bring up this substance 

 in a ready-formed state ; and in the water of the 

 upper strata it is produced by the decomposition of 

 vegetable matter, the iron, both in this and in the 

 water itself, being converted during cellulose fermen- 

 tation into the hydrocarbonate. This compound is 

 then absorbed by osmosis into the bacterial cell, where 

 it is split up by the plasma and oxidised, according to 



. ' ^r ^JC^K' 



g , 



2FeC0 3 + 3H 2 + = Fe 2 (OH) 6 + 2C0 2 



The ferric oxide is then stored up in the sheath, to 

 which it imparts a coloration, initially pale yellow but 

 gradually changing to dark brown. Freshly precipi- 

 FIG. 69. tated ferric hydroxide is, as we know, somewhat 



Clatlothrix dichotoma. soluble in water, but afterwards gradually passes 



Subdivision into roving rods at the into a condition in which it is only attackable by 

 extremity of a thread, s. the weakacids. This change can be traced in the young 

 rods e "vftif 'their 5 (lat^ralTcllia Bacteria, the colouring-matter in the yellow sheath 

 (c). Magn. looo. (After A. being at first extractible by washing with water 

 Fischer.) Cilia staining. containing C0 2 in solution. Subsequently, however, 



dilute hydrochloric acid must bo resorted to, and 



at a still later stage even this solvent is powerless to extract the brown deposit. 

 A very fine and fast blue stain can be produced in young sheaths (the iron in 

 which is still soluble in acid) by exposing them to a mixture of hydrochloric acid 

 and yellow prussiate (potassium ferrocyanide), whereby the hydroxide is dissolved, 

 immediately converted into Berlin blue, and re-precipitated. In older threads 

 the deposits of ferric oxide increase to a thick incrustation, and entirely conceal 

 the structure of the cells. 



Winogradsky discovered that these bacteria thrive only when ferrous carbonate 

 is available, and that growth is arrested directly the nutrient medium contains 

 no iron, or only iron in the condition of oxide. This fact entails the conclusion 

 that the life of these bacteria is mainly sustained by the energy liberated during 

 the oxidation of ferrous oxide to ferric oxide. Consequently, these organisms 

 rightly deserve their name of " iron bacteria." According to the discoveries of 

 H. MOLISCH (I.), iron can be replaced in this oxidation process by the chemically 

 allied metal manganese. These bacteria require but a very small quantity of 

 other nutrient 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. ROSSLEE (I.), that Cladothrix polyspora can be grown 

 on bricks moistened with a little ferrous sulphate solution. In 1894 M. BtSGEN 

 (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. 



