H. B. Hutchinson and J. Clayton 



163 



and various carbohydrates — unsuitable for nutrition of the orj^anism, 

 but some, namely those compounds possessing marked reducing pro- 

 perties, have been found to be toxic even in very low concentrations, 

 e.g. 0-018 per cent, maltose or 0-050 per cent, dextrose. 



As regards the distribution and action of the organism in nature, it 

 might be thought that, by virtue of its sensitiveness to cultural conditions, 

 S. cijtophmja would play a somewhat subordinate role. It is not impro- 

 bable, however, that the conditions obtaining in the soil — aeration, 

 presence of ammoniacal and nitric compounds and of plant residues, as 

 well as the absence of appreciable quantities of soluble organic compounds 

 — constitute ideal conditions for the growth of the organism. 



In this relation to soil biological changes it may be of interest to 

 set up a comparison, between S. cijtoph'Kja and the two other soil forms 

 possessing monotropic relations to carbon compounds — the nitrous and 

 nitric organisms. Such a comparison is made in Table IX, the data 

 respecting the nitrifying bacteria being obtained from Winogradsky and 

 Omelianski's paper^. 



Table IX. 

 Comparison of the Behaviour of Nitrosomonas, Nitrobacter and 

 Spirochaeta cytophaga towards Soluble Organic Compounds. 

 Inhibitory concentrations (per cent.) 



* Calcium salt used. 



<S'. cylophaga is considerably more sensitive than either of the nitri- 

 fying bacteria, practically the sole exception being the high sensitiveness 

 of Nitrosomonas to asparagin. The three organisms have certain common 

 features such as their sensitiveness towards dextrose and their greater 

 intolerance of butyrates than of acetates. It is somewhat remarkable 

 that these three soil forms, two of which obtain their carbon as carbon 



' Winogradsky, S. and Omclianski, W., Cent. Bukt. Par. n. 1899, 5. 436. 



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