150 DR. A. J. EWART ON THE EVOLUTION OF 
rapidly die, but in the light remain living and green—v. e., are 
apparently in darkness erobes, in light anerobes. It is, how- 
ever, as erroneous to call such cases examples of anzrobism in 
Bacteria as it is in green plants. A complete obligate anærobe 
is an organism which not only does not require any supply of free 
external oxygen, but is actually injured by the presence of such. 
All attempts to isolate these green Bacteria by the ordinary 
agar or gelatine-plate method were at first unsuccessful. Plenty of 
uncoloured colonies develop, but these even in light, though they 
may in form closely resemble the green Bacteria, do not become 
green ; and inoculation experiments from these on stagnant water 
which had been sterilized failed to produce any growth of the 
original green Bacteria. Isolation experiments by means of 
plates of agar and gelatine containing inorganic salts, or the 
filtered fluid from stagnant water, were more successful. From 
Bacillus virens cultures, Bacillus colonies were formed on plates 
exposed to light, which in most cases were distinctly yellowish 
and in a few cases slightly yellowish green. The Bacilli are 
often motile, and on plates of gelatine + inorganic salts 
(K,PO,.Am,SO,.MsSO,) form peculiar, somewhat dumbbell- 
shaped concretions of M gCO,. On re-isolating the bacilli on fresh 
plates, or on inoculating in culture-tubes, they develop as before, 
but now, even though exposed to light, are quite colourless. lr 
oculation from these on sterile water produced no green growth. 
With the green Micrococcus-form similar results were obtained. 
Occasionally in both cases a yellowish coloration persists until 
the third inoculation; but from none of the growths on gelatine 
or agar could any distinct evolution of oxygen in light be 
detected. The colonies from the green Streptococcus-form are 
all in the form of Micrococci and not as chains. This, however, 
often takes place with Streptococcus-forms when cultivated on 
nutrient media. Apparently we have here an example of 
extreme pleomorphism—a bacterium which, under normal cor 
ditions, forms chains, is green, and can assimilate, when developed 
on nutrient media becomes colourless, loses the power of assimi- 
lation, and splits up into isolated Micrococci. It is interesting 
in this connexion to notice that a bacterium (Streptococeus 
ochroleucus, Hueppe) is known which in light turns yellow. 
is possible that this may be a closely allied species, variety, °" 
even perhaps the same bacterium as the above S¢reptococ™ 
to which the provisional name of Streptococcus varians may be 
