94 PRINCIPLES OF SOIL MICROBIOLOGY 



to ferric hydroxide is necessary for the life and growth of the organisms, 

 this process furnishing the necessary energy to the cell for the assimila- 

 tion of carbon. According to Molisch, 83 however, Leptothrix will grow 

 well in iron-free media, particularly in peptone solutions, forming per- 

 fectly colorless sheaths. If iron or manganese compounds are present 

 in the solutions, they are oxidized and taken up by the sheaths; even 

 dead cells (killed by boiling) are able to take up ferric hydroxide in their 

 sheaths. He, therefore, concluded that the process is merely physico- 

 chemical and the change of ferrous to ferric compounds is due to simple 

 chemical oxidation and is not connected with the life processes of the 

 cell. Similar observations were made by Ellis 84 and others, 85 who 

 claimed that these bacteria living in iron waters have the power of 

 attracting ferric hydroxide, which is found in quantity in such waters, 

 the deposition of iron being merely a purely mechanical process. This 

 was entirely due to the lack of proper differentiation between the 

 physico-chemical absorption and chemico-biological oxidation of iron, 

 on the one hand, and between the obligate and facultative autotrophy, 

 on the other hand. This led to the general terminology of bacteria 

 which accumulate iron as "iron bacteria," 86 and frequently also to 

 absurdities, as in the case of isolation of a bacterium which can ac- 

 cumulate both iron and calcium (incrustations), where it has been 

 suggested that iron can be replaced by calcium, although evidently no 

 oxidation of calcium is possible. 87 It has, however, recently, been sug- 

 gested 88 that the cells of Gallionella (Spirophyllum) are nothing more than 

 a product of secretion of a small bacterium, 1.2 by 0.5/jl, consisting of 

 two coccus-like cells (0.6 by 0.5/x); the threads themselves consist only 

 of ferric hydrate which dissolves completely in hydrochloric acid, leaving 

 the living cells only at the end of the threads. 



83 Molisch, H. Die Eisenbakterien. Jena. 1910. 



84 Ellis, D. A contribution to the knowledge of thread bacteria. Centrbl. 

 Bakt. II, 19: 507-518. 1907; 26: 321-329. 1910; 31: 499-504. 1911; Iron bac- 

 teria. Science Progr. 10: 374-392. 1916; Iron bacteria. Methuen & Co., London. 

 1919. 



86 Rullman, W. Uber Eisenbakterien. Centrbl. Bakt. II, 33: 277-289. 1912. 

 Zikes, H. Vergleichende Untersuchungen iiber Sphaerotilus natans (Kiitzing) 

 und Cladothrix dichotoma (Cohn) auf Grand von Reinkulturen. Centrbl. Bakt. 

 II, 43: 529-552. 1915. 



86 Lohnis, 1910, p. 704 (p. 28). 



87 Brusoff, A. Ferribacterium duplex, eine stiibchenformige Eisenbakterie. 

 Centrbl. Bakt. II, 45: 547-554. 1916; also 48: 193-210. 1918. 



88 Cholodny, N. Die Eisenbakterien. Beitriige zu einer Monographie. G. 

 Fischer. Jena. 1926. 



