THE IRON-BACTERIA 379 



Schwers, have already suggested that Leptothrix and Gallionella 

 are probably identical. The writer is of the same opinion, and 

 considers that Spirophyllum, Gallionella, and Leptothrix will 

 probably in the future be discovered to be one highly pleo- 

 morphic genus. If so, whatever the factors are which deter- 

 mine the shape, they are brought to bear in the very earliest 

 phases of the existence of each individual. At present, how- 

 ever, we do not possess any evidence in support of the above 

 hypothesis, and we can give expression to what at the present 

 is a matter of feeling and not of fact. 



We are now about to discuss three organisms which likewise 

 form a natural group. They are of greater interest to water- 

 engineers and to medical officers of health than the preceding 

 on account of their tendency to spasmodic immoderate multi- 

 plication causing a serious hindrance to the flow of water 

 through pipes. Their influence on water is not of a pathological 

 nature, no poisonous excretions being liberated as a result 

 of their growth ; but they seriously inconvenience the engineer 

 and give a little anxiety to others who are concerned to see 

 their water reservoirs assume a rusty red colour. We shall 

 not anticipate here the discussion on the physiology of these 

 bacteria further than to state that as a result of their activity 

 the iron which is in solution is precipitated, causing a deposition 

 of ferric hydroxide on all substances with which the water 

 comes in contact. When a certain at present unknown sum- 

 total of conditions holds, these organisms multiply at an 

 extraordinary rate, with the result that the number in the water 

 of individuals each coated with ferric hydroxide is so great 

 that the whole mass of water in a very short time takes on a 

 very disquieting rusty red colour. These sudden rapid multi- 

 plications never last long because the organisms themselves 

 probably make the water unfit for their continued existence. 

 In the intervening period their activities are subdued, in fact 

 they take their place on an equal footing with other water 

 organisms, and it is possible at most seasons of the year to 

 detect their presence by a diligent search in their haunts. 



Crenothrix polyspora (Cohn) 



This organism has been known since 1852, and since then 

 attention to the details of its life-history has been stimulated 



