130 DR. A. J. EWART ON THE EVOLUTION OF 
isolate and develop certain minute green Algæ (Chlorella vulgaris, 
Beyerinck, &c.) on gelatine. 
Were, however, the oxygen evolved by the coloured Bacteria 
a product of an assimilatory process, it would be natural to 
expect that they might be cultivated upon inorganie media or on 
media containing nitrogen and carbon in the form of simple 
organic compounds. The whole of the 9 Bacteria mentioned 
as showing a power of evolving oxygen were inoculated in the 
following solutions :—Sol" A (K,PO, 2 grms.; Am,SO, 5 grms.; 
MgSO, 0:14 grm.; 4000 c.c. H,O). Sol" A+(1) NaHCO,; 
(2) CaCO,CO, ; (3) 3 p. e. grape-sugar ; (4) 4 p. c. cane-sugar; 
(5) 2 p. e. glycerine; (6) 1 p. c. asparagin ; (7) 1 p. c. asparagin 
+2 p. c. glycerine; (8) 1 p. c. asparagin 4-3 p. c. grape-sugar; 
(9) 1 p. c. asparagin 4-3 p e. grape-sugar 4-2 p. c. glycerine. 
In none of these solutions in either light or darkness can the 
coloured Bacteria develop. In 7,8,and 9 a slight trace of almost 
colourless sediment may be found, but in all the others not the 
least growth takes place. These Bacteria all develop normally 
and abundantly only on nutrient media containing peptone. 
On peptone-agar and peptone-gelatine they develop well and form 
abundance of pigment without any sugar being necessary, but 
in bouillon cultures the presence of sugar slightly favours their 
growth and pigment formation. They are all pronounced obligate 
saprophytes. 
Other results also tend to show that the oxygen evolved is not 
the product of a process of assimilation. Thus the evolution of 
oxygen apparently continues as actively and persists for as long 
a time in the darkness as in the light. This might, howeven 
really be due to the evolution of oxygen recommencing instal 
taneously on re-exposure to light. For comparative purposes 
gelatine preparations of Protococcus, Scenedesmus, &c. were made 
and examined. These show at the edge of the gelatine an activé 
evolution ofoxygen. In darkness, in under 5 minutes the Bacte 
rium Termo come completely to rest, and on re-exposure to light 
recommence to move in 15-30 seconds (according to the thickness 
of the rim of gelatine between the outermost algal cells and the 
surrounding B. Termo), and are in fully active movement in 1-4 
minutes. With gelatine preparations of Bacillus brunneus the 
evolution of oxygen is on re-exposure to light seen to be normally 
active however instantaneous the examination may be, ? 
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