4 
Macgregor Skene. 
When one considers these different views, one must admit 
that the results of Winogradsky are still the most worthy of 
attention. Although he worked with drop cultures only, he 
obtained a very clear insight into the necessities of the organisms 
he studied. Nevertheless the problem cannot be regarded as 
solved. Only pure cultures permit of a complete comprehension of 
the physiology of nutrition of micro-organisms. Pure cultures have 
unfortunately not yet been obtained; in the following paper, 
however, I wish to describe the results of experiments with, and 
of observations on mixed cultures, which may help in some degree 
to extend our knowledge of the physiology of the purple sulphur 
bacteria. 
I—Material and Culture Methods. 
Purple sulphur bacteria may be easily obtained, and cultivated 
under more or less natural conditions. According to Winogradsky 
it is only necessary to place pieces of Butomus rhizome in a deep 
glass vessel, fill up with water, and add some calcium sulphate, in 
order to obtain in the course of a few weeks a fine development of 
purple bacteria on the walls of the vessel: the appearance of the 
purple zoogloea is always preceded by a considerable evolution of 
hydrogen sulphide. I found this method to answer well in 
Strassburg 1 ; but it failed when 1 tried it in Aberdeen. Consequently 
most of my experiments were carried out with sulphur bacteria 
from the salt-marshes near Kiel, material of which was very kindly 
sent me by Professor Dr. E. Lehmann, to whom I am much 
indebted. The water of these marshes contains 0-6% sodium 
chloride, but I found that the bacteria grew perfectly in water 
containing 2-7%, and all my culture solutions contained that 
quantity 2 . A continuous abundant supply of material is easy to 
maintain. A large (3 litre) wide-mouthed bottle is filled with 
salt water, to which is added about 30 grms. of chalk and 5 to 10 grms. 
of calcium sulphate: a few lumps of Enteromorplia are thrown in, 
and the liquid is innoculated with the sulphur bacteria. Hydrogen 
sulphide is rapidly produced by the reduction of the calcium 
sulphate, and probably also by the putrefaction of the Enteromorplia, 
and, if the bottle be placed in the light, a vigorous development of 
sulphur bacteria takes place in from two to four weeks according to 
the season. The zoogloea is thick, opaque, and of a fine red-purple 
1 Where Winogradsky’s research was carried through. 
2 As that happened to be the concentration in the raw culture most 
suitable for using as infection material when I started my decisive cultures. 
