158 Decoitiposition of Cellulose 



lower limits of growth are probably associated with minimum nitrogen 

 requirements, since the more highly nitrogenous salts give better growth 

 than sodium ammonium phosphate. On the other hand, the upper 

 limits of growth do not appear to be determined by nitrogen concen- 

 tration, since sodium nitrate gives as good results as sodium ammonium 

 phosphate, although it contains about 2| times as much nitrogen. It 

 is also to be expected that the favourable effect of sodium nitrate is a 

 complex one, i.e. with increasing abstraction of nitrogen the reaction of 

 the solution would be better maintained owing to the formation of 

 sodium carbonate or of neutral salts of acid by-products. 



A supplementary set of experiments included the use of a number of 

 the simpler organic nitrogen compounds which, from their constitution, 

 might be expected to serve as sources of nitrogen. Two concentrations 

 were tested, viz. 0-5 and 0-05 per cent., the general method being to 

 add the test solution to the slightly alkaline mineral salt solution after 

 sterilisation, thus reducing the risk of decomposition of the compound. 

 The results are given below (Table IV). 



The majority of the compounds are thus suitable for growth, although 

 their values are widely different. The behaviour in urea is peculiar and 

 requires further investigation, but from the jjaucity of growth in the 

 initial stages and the abundance of growth after 40 days it might be 

 assumed that acclimatisation to the compound took place, or that the 

 power of hydrolysing the urea was eventually acquired. The results 

 with hydroxylamine sulphate and hydrazine sulphate are in conformity 

 with the frequently observed intolerance of S. cytophaga of any reducing 

 substances. Acetamide and asparagin give poof results in low con- 

 centration but fairly good effects when present to the extent of 0-5 j^er 

 cent. Formamide, on the other hand, is apparently of value only in 

 low concentrations (0-05 per cent.), and acts inhibitively in strengths 

 approaching 0-5 per cent. 



Relations to various Sources of Carbon. 



The carbon requirements of the constituent species of the soil flora 

 may be met by a considerable range of compounds — from carbon dioxide 

 through the paraffins, alcohols, fatty and hydroxy- acids, and the various 

 monoses and bioses. Of these, such compounds as glycerol and mannite, 

 maUc, citric, succinic and tartaric acids, dextrose, maltose and sac- 

 charose are of the most general utility. At the same time several of the 

 species exhibit a high degree of specificity as, for examjDle, the nitrifying 

 organisms and some of the sulphur bacteria. On this account, and in 



