Physiology of the Purple Sulphur Bacteria. 15 
goes on more quickly, and after five to six weeks the development 
in the blue is as good as in the red. Whether this is to be referred 
to the action of the blue rays, or of such red rays as penetrate the 
filter, cannot be definitely stated. But in any case it is certain that 
if the red rays of ordinary daylight are not alone effective, at least 
they are much more so than are the blue. 
For the sake of comparison I tested the two filters with Elodea, 
by means of the gas-bubble method. The relative photosynthetic 
activity of daylight: red : blue, was about 6:3: 1. 
Why light should be necessary for the development of the 
sulphur bacteria we are not yet in a position to say. If we had an 
exact demonstration of the capacity of the bacteria to assimilate 
carbon dioxide, we might well regard the action of light as being 
bound up with the process. But as the matter stands we cannot 
well build theories on the fact that red light is more effective than 
blue. It is also by no means certain that Bacteriopurpurin, the red 
pigment, is a true chromophyll. 1 
V.— The Relation of Oxygen to the Purple 
Sulphur Bacteria. 
Different investigators have expressed very different views on 
the relation of the sulphur bacteria to oxygen. As already remarked 
Nadson regards them as anaerobic. Molisch and Winogradsky on 
the other hand consider that they require small quantities of oxygen. 
As Winogradsky was able to show, in a convincing manner, 
that they continually carry on an oxidation of hydrogen sulphide to 
sulphur, and of sulphur to sulphuric acid, and that they carry out 
this oxidation in absence of any oxidising agent such as potassium 
nitrate, it seems to follow necessarily that they require a supply of 
oxygen. How this supply can be obtained, in situations where there 
is always present a considerable amount of sulphuretted hydrogen, 
is the problem. 
Winogradsky observed that the forms with which he worked 
always lived in the neighbourhood of little groups of very small 
rods and cocci, which were bright green in colour. He believed 
that the photosynthetic activity of these resulted in the liberation 
of a sufficient quantity of oxygen to serve the needs of the sulphur 
1 Molisch’s statements (1907) concerning Bacteriopurpurin, in so far as 
they may refer to Amoebobacter and Lamprocystis, are not exact: if a piece of 
zoogloea is placed in absolute alcohol then, whether the treatment is in heat or 
cold, a solution is obtained which is brick- to purple-red, and certainly not green. 
A separation of the Bacteriochlorin and the Bacteriopurpurin in this solution 
is readily carried out by capillary analysis. A drop of the solution placed on 
filter-paper forms a bright red patch with a narrow, sharply differentiated, 
bright green margin. 
