SnD > 
1899 | PRODUCTION OF FLUORESCENT PIGMENT 23 
The most extended contribution to our knowledge of the 
fluorescent bacteria, with the exception of Gessard’s classic 
papers upon B. pyocyaneus, is contained ina paper by Thumm.*% 
My own observations conflict with Thumm’s at some points, 
while the conclusions I am compelled to draw from my results 
are, in important respects, so at variance with his that I do not 
hesitate to reopen the whole question and to present the record 
of my experiments in some detail. 
INFLUENCE OF THE CHEMICAL COMPOSITION OF THE MEDIUM. 
In 0.2 per cent. pure asparagin solutions a very slight tur- 
bidity occurs, but no trace of color. If 0.1 or 0.5 per cent. of 
chlorid (sodium, calcium, magnesium, or potassium) be added to 
the asparagin solution, the turbidity is slightly increased, but no 
pigment is formed. Sulfates (sodium, magnesium, or potassium) 
in the same proportion aid the growth more than chlorids, but 
no color appears. Pure phosphates (sodium, magnesium, or 
potassium) are yet more favorable to growth, but fluorescent pig- 
ment still fails to develop. I must at this point lay stress upon 
the importance of obtaining chemically pure phosphates. A 
mere trace of sulfate in the presence of phosphate, as I shall 
show presently, is sufficient to lead to the production of pigment. 
I have found that many samples of “C.P.” phosphate obtained 
from reliable manufacturers contain a quantity of sulfate suffi- 
cient to vitiate the results, and I have consequently been compelled 
to prepare pure phosphates by recrystallization or by thorough 
washing. 
If the various species be grown in a solution of 0.2 per cent. 
asparagin, 0.I—0.5 per cent. sodium (or magnesium ) chlorid, and 
0.1 per cent. neutral sodium phosphate, the resulting turbidity 
is but little, if at all, greater than in the asparagin -phosphate 
solution alone. If, however, 0.1 per cent of sulfate (sodium, 
"3 Beitriage zur Biologie der fluorescierenden Bakterien. Arb. d. Bakteriol. Inst. 
d. grossh. Hochschule zu Karlsruhe, 1895. 
**T am indebted to my friend Professor Stieglitz for many suggestions regarding 
the preparation and testing of pure salts. 
