442 



Mr. W. T. Lockett. Oxidation of 



containing ammonium sulphate (0\L per cent.) and sodium thiosulphate 

 (0 - 4 per cent.), that a great number of slow growing, circular, non-liquefying, 

 bluish-white colonies were obtained. 



Plates made with such a medium showed that active filtrates contained 

 100 to 1000 times more organisms per cubic centimetre than was shown on 

 gelatine and agar. In addition the microscopic appearance of the organism 

 was apparently identical with those previously noted in the slides of the 

 filtrates. 



Streak cultures of the organism made on media of the same composition as 

 the above produced clearly defined, thin, bluish-white growths after 10 to 

 15 days' incubation at 20° C. 



Experiments were then made to ascertain how far this particular organism 

 was able to bring about the oxidation of thiosulphate. At first difficulties 

 arose with regard to the finding of a suitable liquid medium for the growth of 

 the organism ; eventually good growths were obtained by the use of a medium 

 of the following composition : — 



r0 grm. sodium thiosulphate, - 5 grm. ammonium sulphate, - 5 grm. 

 potassium biphosphate, - 025 grm. sodium chloride, - 01 grm. magnesium 

 sulphate, 2'0 grm. Eochelle salt, dissolved in 1000 c.e. distilled water. 



To this solution it was found necessary to add sufficient acid (N H 2 S0 4 ) to 

 reduce the alkalinity to methyl orange by approximately one-half, thereby 

 presumably liberating free tartaric acid. Before and after sterilisation clear 

 solutions were obtained of this mixture, which were alkaline to methyl 

 orange: 



A suitable solid medium for the growth of the organism is also obtained by 

 the addition of gelatine ^10 per cent.) to this solution. 



In testing the oxidising power of the organism the procedure generally 

 adopted was as follows : — A pure streak culture was taken, and a small 

 quantity of the growth, attached to the end of a sterile platinum needle, was* 

 introduced into 10-12 c.c. of the above sterile solution contained in a test- 

 tube, the usual bacteriological precautions being observed. 



After a few days' incubation at 20° C. a slight white, stringy growth was 

 observed in the inoculated solutions. Later, after 14-21 days a distinct 

 turbidity was apparent, and the solutions on examination at this period were 

 found to be free from thiosulphate. Complete oxidation had taken place with 

 the formation of acid sulphate, the final solution being slightly acid to methyl 

 orange. 



Uninoculated solutions showed no change after several weeks' incubation. 

 A large number of experiments have been made on these lines with 

 complete success. Solutions inoculated directly from colonies found on 



