144 DR. A. J. EWART ON THE EVOLUTION OF 
power of occluding oxygen be detected. These are :—Bacillus 
miniacus (colour varying—red, purple, blue, white); Bacillus 
cyanogenus (blue); Bacillus fluorescens; Micrococcus bicolor; 
Micrococcus candicans; Bacillus indigonaceus (greenish blue); 
Spirillum rubrum, S. undula, S. tenue ; Bacterium Termo ; Micro- 
coccus prodigiosus (red); Bacillus pyocyaneus (blue—yellow); 
Chromatium Okenii (purple) : Bacillus virens (green); Strepto- 
coccus varians (green) ; and Bacterium photometricum (brownish 
red to reddish purple). 
This property of absorbing and then, under reduced partial 
pressure, slowly evolving oxygen is a property not of all, but 
only of certain coloured Bacteria, in all of which the pigment is 
a Lipochrome. A very interesting question is whether this is 
a universal property of all lipochrome pigments—mono-, di-, and 
tetra-carotin. It is interesting to notice that Arnaud gives as 
the formula for carotin as extracted from Phanerogamic leaves 
C,,H,,; whilst Husemann states that carotin contains 6 p. c. of 
oxygen and gives it the formula C,,H,,O,. It might be possible 
that the oxygen thus found by Husemann was held in a state of 
combination similar to that in which a portion of the oxygen is 
held by oxyhemoglobin. The isolated bacterial pigment was 
found to evolve at most per gramme of dry weight 0°7 c.c. of 
oxygen. Supposing that, if pure, the amount evolved might 
have reached 1 c.c. and been nearly equal to that of hemo- 
globin (4 grms.—42 c.c.), this would only have given per 
moleeule of pigment (according to Husemann's formula) 0032 
of an atom of oxygen. The highest amount evolved from the 
Bacteria themselves per gramme being taken as O-4 c.c., and 
supposing that the pigment forms about iy of this weight, and 
therefore in this case can evolve per gramme 4 c.c. of oxygen 
this would, however, only give per molecule of pigment about 
0:13 of an atom of oxygen. These amounts are quite insufficient 
to support the above hypothesis; and since the formula given by 
Arnaud seems to be the correct one, it is probable that Husemann 
did not work with the pure pigment. It is, however, very 
evident that further research in this direction from both 4 
chemical and a physical standpoint is urgently needed *. 
* The chemical and physical study of the bacterial pigments is being 
continued in the Botanical Laboratory of Leipzig University by Dr. Kunath 
and Prof. Pfeffer, 
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