Physiology of the Purple Sulphur Bacteria. 17 
2. In mixed cultures Amcebobacter (and probably also Lampro- 
cystis) thrives best in a mineral solution, containing ammonium 
sulphate as a source of nitrogen, and with chalk as a neutralising 
agent. 
3. All the organic sources of nitrogen and carbon which were 
investigated, proved to he without favourable influence on the 
growth of the bacteria : on the contrary, as a rule, they tend to 
inhibit development. 
4. A loose symbiosis with autotrophic thiobacilli is possible, 
but does not seem likely. 
5. Development can only take place in presence of hydrogen 
sulphide: this cannot be replaced by other sulphur compounds. 
6. Growth only takes place in light: red light is more effective 
than blue. 
7. The purple sulphur bacteria require free oxygen which is 
probably supplied in nature by associated green organisms. 
The investigation was commenced at the suggestion of Professor 
Dr. Ludwig Jost in Strassburg. It is a great pleasure to express 
my thanks to Professor Jost, for the help and criticism he has 
always placed at my disposal, both when I was in Strassburg, and 
since my return to Aberdeen. 
LITERATURE. 
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3. Engelmann, Th. W., 1888. Bot. Ztg. 46, 661. 
4. Keil, F, 1912. Beitr. z. Biol. d. Pflanz. 11, 335. 
5. Lankester, E. Ray, 1873. Quart. Journ. Microscop. Science 13, 408. 
6. - 1876. Ib. 16,27. 
7. Lidforss, B., 1912. Ber. d. deutsch. bot. Ges. 30, 262. 
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11. Molisch, Hans, 1907. Die Purpurbakterien (Jena). 
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