3 
Physiology of the Purple Sulphur Bacteria. 
require a clay or more for a single division, and (b) because the 
organic food substances are used only for body-building, energy 
being supplied solely by the oxidation of the hydrogen sulphide. 
Since Winogradsky three investigators have busied themselves 
with the subject. Engelmann (1888), using his well-known “ bacterium 
method,” endeavoured to show that the sulphur bacteria give off 
oxygen in light. He considered that he had succeeded in doing so, 
and consequently held that sulphur bacteria w T ere capable of photo¬ 
synthesis, and that their red pigment played a part corresponding 
to that of chlorophyll in the higher plants. 
His conclusions and his experimental data have been attacked 
from two sides. Winogradsky himself regarded them as improbable 
for purely theoretical reasons. Molisch (1907), in a monograph on 
Purple Bacteria, reinvestigated the question experimentally, and 
could not confirm Engelmann’s results. 
It is somewhat difficult to form an opinion on the part of 
Molisch’s book which touches on the sulphur bacteria. He deals 
not only with the purple sulphur bacteria, but also with a number 
of others, which seem to have only the possession of the pigment 
in common with the hydrogen sulphide oxidising organisms. He 
obtained pure cultures of several species ( Rhodobacillus, Rhodo- 
bacterium, etc.), which do not have the property of storing up sulphur 
globules. These thrive in solutions of organic food substances 
(1% peptone + 1% dextrine), grow better in light than in darkness, 
require no hydrogen sulphide, and are microaerophil. 
He makes but few references specially to the sulphur-storing 
forms; but remarks that Chromatium grows well in the peptone- 
dextrine solution, and shows only a very slight development, if any, 
without peptone. But it must be added that on reading through his 
book, one has the impression that Molisch believes the sulphur 
bacteria to behave as do the other purple forms—that is, that they 
require organic food substance, and do not require hydrogen 
sulphide. 
Finally, there must be mentioned a paper by Nadson (1903). 
From the results of one or two raw cultures he comes to the 
conclusion that hydrogen sulphide is unnecessary, and that in 
nature it serves only as a protection against oxygen. His experi¬ 
ments are few in number, and as they deal chiefly with bacteria 
showing no sulphur inclusions (only in one case were scanty 
granules observed), it is doubtful whether his conclusions can be 
applied to the sulphur bacteria in general. 
