7 
Physiology of the Purple Sulphur Bacteria. 
course forms a sediment), be infected with sulphur bacteria, and 
placed in the sulphuretted hydrogen atmosphere, then in the course 
of 10 to 30 days, according to the season of the year 1 , a vigorous 
development of the bacteria takes place. The chalk sediment 
becomes covered with a rich red-purple zoogloea. 
Source of Nitrogen. 
The following substances were tested :— 
Egg albumen. 
Peptone. 
Asparagine. 
Glycocoll. 
Urea. 
Ammonium nitrate. 
Ammonium sulphate. 
Calcium nitrate. 
These substances were employed in a concentration of 0-08% in 
addition to the mineral constituents of Lieske’s solution, less of 
course the ammonium sulphate. As a control cultures without 
nitrogen were infected. The egg albumen was added in the form 
of lumps of boiled white of egg. The necessary salt and chalk 
were added. For each culture a flask and two test tubes were 
used. 
After three weeks, the result was that the growth in ammonium 
sulphate was best: albumen, peptone and asparagine were only 
slightly less favourable: a slight development was observed in urea: 
in glycocoll, ammonium nitrate, and calcium nitrate no growth had 
taken place. One might conclude from this, that peptone, 
asparagin and albumen formed as satisfactory sources of nitrogen 
as ammonium sulphate. When, however, the various solutions 
were tested with Nessler’s Reagent, at the end of the experiment, 
it was found that these three gave almost as strong a reaction as 
the ammonium sulphate; further that urea gave a slight reaction ; 
while glycocol—and of course calcium nitrate—gave negative 
results. This must be referred to a production of ammonia from 
the various compounds in question under the action of other 
bacteria which are present in these mixed cultures : ammonium 
nitrate appears to be strongly toxic. 
The same series of nitrogenous compounds was tried with 
025% solutions of calcium lactate and of mannite : the results 
’ The varying of the rate of development with the change of the season 
depends on the amount of light available, and is not concerned with temperature 
changes. 
