6 
Macgregor Skene. 
red zoogloea: it was accompanied by abundant Amcebobacter roseus: 
less plentiful were Thiopolycoccus ruber and Thiothece gelatiuosa. 
In the conical flasks on the other hand Amcebobacter roseus was 
always most abundant, being accompanied chiefly by Lamprocystis 
roseo-persicina. The following observations should therefore be 
taken to apply to Amcebobacter. 
II —The Food Requirements of the Purple 
Sulphur Bacteria. 
As has already been remarked Winogradsky expressed the 
opinion that the purple sulphur bacteria required organic food- 
substance, but only in minimal quantities: in his drop cultures he 
used Strassburg tap water (which contains very little organic 
substance) to which he added 0-005%—0-01% calcium butyrate or 
sodium acetate: no better growth was obtained with peptone or 
beef extract. Molisch on the other hand maintains that Chroma- 
tium will only grow in solutions containing 1% peptone + 1% 
dextrine. Apart from these unsatisfactory, and contradictory 
statements, there is to be found in the sulphur bacteria literature 
absolutely nothing on the question of food requirements. 
In order to determine the best conditions for the development 
of the bacteria, I carried out a long series of comparative cultures 
in different nutrient solutions, and I can fully confirm Winogradsky’s 
statements, in so far that I could never observe the slightest 
improvement in the growth of the bacteria resulting from the 
addition of organic compounds. 
It may be stated at once that the quickest and most vigorous 
development took place when the bacteria were provided with a 
solution, the constitution of which differed only slightly from that 
employed by Lieske (1911), for the culture of the Iron Bacteria: it 
had the following constitution :— 
Ammonium sulphate 
0*75 
grms. 
Magnesium sulphate 
0-05 
yy 
Potassium dihydrogen phosphate 
0-05 
Potassium chloride 
005 
yy 
Calcium nitrate 
0-01 
yy 
Sodium chloride 
27-0 
yy 
Calcium carbonate 
10-0 
yy 
Distilled water ... 
1000 
CCS. 
If a small conical flask (50 to 100 ccs.) be provided with as much 
of this solution as forms a layer 1 to 1£ cms. deep (the chalk of 
