Glucose and Mannitol hy B. coli communis. 



77 



found to assist the fermentation when added to the emulsion of bacteria 

 washed off the surface of the agar. Such ions if necessary are required only 

 in the traces in which they exist in the emulsion so obtained. 



The metallic ions added were those of manganese, iron, zinc and aluminium ; 

 the negative ions, chloride, nitrate, silicate and phosphate. 



The writer has found that in order to grow B. coli communis on an artificial 

 medium such as a solution of sugar and mineral sulphates together with some 

 source of nitrogen such as ammonium sulphate or an amino-acid (asparagine, 

 alanine, glycine) it is necessary or at least highly beneficial to add a phosphate ; 

 nevertheless no beneficial effect was obtained upon the rate of fermentation 

 when phosphates were added to the fully grown organisms. 



A solution of 6 grm. of potassium sulphate and 0"5 grm. of magnesium 

 sulphate per litre is suitable for the study of the decomposition of substances 

 allied to glucose under the influence of £. coli commimis. 



If each of the Eoux bottles contain about 100 c.c. of agar and the growth 

 be obtained in the manner described, it will be found that 10 bottles will yield 

 about 1 grm. of dried bacilli. The amount of organic matter outside the bodies 

 of the bacteria which is washed off the agar with the potassium sulphate 

 solution has been found to be fairly constantly equal to three times the weight 

 of the yield of dried bacteria. The weights of dried bacteria and soluble 

 organic matter are determined for each experiment by centrifugalising a 

 sample of the emulsion and determining the weight of bacteria directly, and 

 the organic matter in the solution by evaporation in a platinum vessel and 

 weighing after drying at 110° C. and after incinerating, or the bacteria may 

 be determined indirectly by evaporating to dryness two separate samples, 

 from one of which the bacteria have been separated by the centrifuge. The 

 difference in weight represents the weight of bacteria in the sample of 

 emulsion. 



Arrangement of Apparatits for the Study of a Complete Fermentation. 



The fermentation flask rests in the water-bath, regulated for the required 

 temperature. The flask has a capacity of about 2 litres. The volume of the 

 ■fermentation solution at the beginning of the experiment is about 1| litres. 

 At the end of the experiment water is introduced to displace the gas above 

 the solution in the flask. 



In the experiments described below the procedure adopted was as follows : 

 The flask containing chalk and the substance to be fermented dissolved ii 

 about 800 c c. of distilled water was sterilised by heat. The solution was 

 cooled to 38° C. and the emulsion of bacteria introduced, the amount added 

 •being determined by weighing the flask before and after the introduction of 



H 2 



