August 5, 1920] 



NATURE 



727 



Iron- depositing Bacteria.^ 



^p HE appeal of the monograph before us, which is 

 -»• one of the Professional Papers issued under the 

 aegis of the United States Geological Survey, will 

 probably be of direct interest only to a comparatively 

 small section of scientific workers. Although there is 

 much to attract the general reader, it is obvious 

 that the work was not initiated with this end in 

 view. It is worthy of note and a sign of the times 

 that the data supplied by the bacteriologists should 

 be used as a serious, weapon of offence in attacking 

 a geological problem. 



Many changes, due to biological influences, take 

 place on the earth's surface which profoundly modify 

 the constitution of the material which is destined 

 to become the geological strata of the future. A 

 study of these changes will obviously throw light on 

 the causes which have operated in the past to bring 

 the earth's crust into being. We find in Mr. Harder's 

 paper by far the most comprehensive treatment 

 which we have yet seen of the activities of bacteria 

 in effecting chemical changes in various iron com- 

 pounds which come within the scope of their influence. 

 He has undertaken the task of bringing together in 

 the form of a critical survey the salient facts of 

 our knowledge of the iron bacteria. This subject 

 occupies the first half of the monograph, and is 

 treated by the author with a masterly regard for 

 essentials, and in it is included the results of some 

 of his own observations and experiments on these 

 interesting micro-organisms. It is interesting to note 

 that the sarne iron bacteria are found in America as 

 in Europe, although there are slight differences in 

 their distribution and numbers. Thus Spirophyllum 

 ferrugineum appears to possess a wider distribution 

 than is the case in this country. 



In the preface, which is written by Mr. F. L. 

 Ransome. especial attention is directed to the results 

 of Mr. Harder's inquiry into the physiology of the 

 iron bacteria. Hitherto each investigator has assumed 

 that the results claimed by him as a result of his 

 research on the physiology of some particular species 

 held good for all the iron bacteria. Mr. Harder, how- 

 ever, concludes that there are three principal groups 

 of iron-depositing' bacteria : (i) A group the members 

 of which precipitate ferric hydroxide from solutions 

 of ferrous bicarbonate. (2) A second group of iron 

 bacteria that does not require ferrous bicarbonate for 

 its vital processes. (3) A third group that attacks 

 iron salts of organic acids, using the organic acid 

 radicles as food and leaving ferric hydroxide, or basic 

 ferric salts that gradually change to ferric hydroxide. 

 We must confess to a scepticism as to the existence 

 of such deep-seated differences among these organisms, 

 and incline to the opinion that the phenomenon of 

 iron-deposition on micro-organisms shows the work- 

 ing of a simple physiological law which operates on 

 all in the same manner. In support we would 

 advance the fact that Spirophyllum and Leptothrix 

 are so cl6sely allied that some have regarded them 

 as pleiomorphic varieties of one and the same 

 organism. They live in the same waters, they repro- 

 duce alike, and are in every way similar except in 

 external form ; and yet Spirophyllum is stated to be 

 an example of the first group, whilst Leptothrix is 

 relegated to the second group. A more cogent ground 

 for scepticism lies in the fact that other organisms, 

 including some of the algae and the protozoa, possess 

 the same attraction for iron compounds. Possibly a 

 closer investigation of the chemko-irritability of 

 micro-organisms will throw some light on the 

 question. 



1 " Iron depositing Bacteria and their Geologic Relations. " By PCdmund 

 C. Harder. United States Geological Survey. Professional Paper 113. 



NO. 2649, VOL. 105] 



We can recommend the second half of the mono- 

 graph to all who wish concise information from an 

 authoritative source of the iron deposits of the world 

 and of the factors which influence the formation and 

 determine the mode of deposition of the iron precipita- 

 tions that are taking place at the present day. With 

 one exception iron is the most abundant element in 

 the earth's crust. Iron salts are being constantly 

 decomposed, and the genesis of the active agents 

 which bring about their decomposition is given in 

 detail. A consideration of these agents brings home 

 to us the necessity of studying the life-histories of 

 various micro-organisms in order to understand how 

 the present deposits came into being. To give one 

 example. The most important of the iron deposits 

 is ferric hydroxide, and a study of the conditions of 

 its formation centres largely round the fact that 

 ferrous compounds are soluble in water containing 

 CO2 in excess. Now, in particular, ferrous bicarbonate 

 percolates upwards in solution, and when it reaches 

 the surface becomes subject to the interplay of forces, 

 both chemical and biological, which determine its 

 subsequent fate. We must refer the reader to the 

 work itself for more precise information regarding 

 the manner in which this fate is determined. 



We are also given a very complete account of the 

 various types of ferruginous sedimentary ores, and 

 in each case the intervention of biological agencies, 

 either in the primary or in the secondary rdle, as 

 factors in the determination of the final deposition is 

 explained in a comprehensive and accurate manner. 

 Of greatest interest of all is, we consider, the 

 examination of the conditions which determine the 

 formation of bog-iron ore. These are undoubtedly 

 mainly of a biological nature, and deserve more con- 

 sideration than they have hitherto received. The interest 

 in this ore is enhanced on account of its formation 

 being a possible stepping-stone to the development of 

 limanites and haematites, although Mr. Harder him- 

 self has not raised the point. In his reference to the 

 ferrous carbonate deposits he does well to speak with 

 reticence of the factors which have brought about 

 their formation ; enough evidence, however, is 

 advanced to give pause to those who would eliminate 

 altogether the activities of micro-organisms from the 

 list of active agents which have brought these deposits 

 into being. Again, Mr. Harder makes out a clear 

 case for the intervention of micro-organisms in the 

 formation of some, at any rate, of the iron sulphide 

 deposits. Sulphuretted hydrogen is evolved as a result 

 of the decomposition of animal and vegetable matter 

 bv the saprophytic bacteria. The formation of sul- 

 phides with iron compounds is the next step, and it is 

 of great interest that we see the process at work at 

 the oresent dav in the development of the "blue mud" 

 of the ocean bottom. 



Both biologists and geologists will be grateful to 

 Mr. Harder for the work which he has done in the 

 preparation of this monograph. David Eilis. 



The Association of Technical Institutions. 



'X'HE Association of Technical Institutions opened 

 "*■ its summer meeting at the University of Cam- 

 bridge on July 23, with the Marquess of Crewe, the 

 president, in the chair. The meeting was extended 

 over the following day, when the chairman of 

 the council, Mr. Dan Irving, M.P., presided. 

 Papers were submitted on "A National System 

 of Education," by Principal J. C. M. Garnett 

 (Manchester); on "The Necessity for Close Co-opera- 

 tion between Technical Colleges and the Universities," 

 by Principal C. Coles (Cardiff); on " Continuation 



