Ward . — A Violet Bacillus from the Thames. 73 
so trivial that I am strongly inclined to regard them as acci- 
dental. Eisenberg’s description of the plate- and other 
gelatine-cultures, of the development of the membrane on 
agar and broth, absence of spores, and so on, are quite like 
mine ; but the rods are extremely short, and non-motile, 
though their thickness agrees very well. His description of 
the potato-cultures also agree with some of mine, though in 
other cases I find the pigment developed on these also. 
On the whole, it seems pretty certain that this violet 
Bacterium from the Thames is, then, the one found by 
Jolles in water, and named B. membranaceus amethystinus by 
Eisenberg. 
Other Pigment-Bacteria, with blue or violet hues, are 
referred to in the literature, but the descriptions are so 
incomplete that I cannot compare them. Thus Schroter’s 
B. Lacmus 1 , Ehrenberg’s B. syncyanus 2 , Beyerinck’s B. cyaneo - 
fuscus 3 , forms a blue pigment in one of its stages, but does 
not properly come under the head of violet Bacteria. What 
Jordan’s B. cyanogenus 4 is, and whether it is the same as 
Hueppe’s 5 Bacillus of blue milk, I cannot decide, but both 
may safely be regarded as distinct from any of the forms 
referred to, and the pigment is quite different. The same 
is true of Alvarez’ B. indigogenus* , and so far as I can 
discover these exhaust the list of blue and violet Pigment- 
Bacteria. 
It not unfrequently happens that plate-colonies refuse to 
colour. I have made numerous attempts to determine the 
cause of this. Exposure to light, and cultivation at too high 
a temperature, may bring it about, and in one series I had it 
in culture for nearly a year as a white or slightly yellowish 
form which refused to form the violet pigment. Eventually, 
however, the colour appeared in a milk-culture, and was 
1 Pilz. Schles., p. 158, referred to by De Toni and Trevisan in Saccardo’s Syll., 
Vol. viii, p. 978. 
2 Verhandl. d. Berl. Akad., 1840, p. 202, and Saccardo, 1 . c., p. 979. 
3 Bot. Zeit., 1891, No. 43. 4 Jordan, 1 . c., p. 832. 
5 Mitth. aus dem Kaiserl. Ges., Bd. ii, p. 355 (see also Heim, ibid., Bd. v, p. 518). 
6 Sternberg, Bacteriology, 1893, p. 476. 
