Physiology of the Purple Sulphur Bacteria. 11 
could he noted were in favour of those not previously infected 
with the bacillus, next came the sterilised, and finally those which 
were provided with a living bacterial flora. A second series gave 
precisely similar results. 
From these experiments we may conclude that under the 
conditions in question the autotrophic bacilli have no favourable 
influence on the growth of the purple sulphur bacteria : the evidence 
is not conclusive, as a smaller number of the bacilli might be a 
necessary condition, but it has at least some probability and so 
cannot be left out of consideration. 
Some Methods by which Pure Cultures were Sought 
to be Obtained. 
The trials were chiefly concerned with the possibility of growth 
on solid substrata. Winogradsky (1888) remarks that growth does 
not take place on gelatine, but does not enter into details: in 
particular be does not mention the culture media employed, nor 
whether he supplied sulphuretted hydrogen to his cultures—only 
that in gelatine the sulphur bacteria perish rapidly. It was 
therefore advisable to investigate as many solid media as 
possible :— 
1. Agar -f- Lieske’s solution. 
2. Agar -f- peptone 0-5% + dextrose 0-5%. 
3. Gelatine + Lieske’s solution. 
4. Gelatine + Enteromorpha extract. 
5. Silica jelly -f- Lieske’s solution. 
6. Plaster of Paris + Lieske’s solution. 
7. Filter paper -f- Lieske’s solution. 
All received the requisite quantities of salt and chalk: nos. 1-5 
were infected by painting the surface and also in the usual manner 
by pouring plates. Hydrogen sulphide was supplied as usual. 
Unfortunately all these media gave negative results. 
There are three possible explanations of this failure:— 
1. The medium may contain too much organic substance 
(agar and gelatine): but this does not apply to nos. 5-7. 
2. Neutralisation may be too slow, when the chalk is embedded 
in a jelly. Here we may remark that the diffusion of acid in a jelly 
is quite rapid. I was unable to replace the chalk by a soluble 
carbonate. Sodium bicarbonate and potassium carbonate appear 
to be toxic in small concentrations: 0 - 25 % of the former was 
sufficient to inhibit growth almost completely. 
