ee ee ee ee ee Bath 
1899] PRODUCTION OF FLUORESCENT PIGMENT 33 
explicable on the supposition that a small amount of sulfate was 
present as an impurity in the latter salt. 
2. Lhe nature of the base associated with the phosphorus and sulfur 
2s not tmportant. 
Thumm observed, as I have done, that the omission of calcium 
chlorid alone from a nutrient solution containing potassium phos- 
phate and magnesium sulfate exerts no perceptible effect on the 
production of pigment, but that the omission of the magnesium 
sulfate alone causes a marked diminution in pigment production ; 
in my own experiments a total inhibition. From this he draws 
the singular conclusion that ‘so far as the formation of pigment 
is concerned, magnesium cannot be replaced by calcium.” It is 
not necessary to point out the fallacy involved in such a 
deduction. 
3. The conclusions that may be drawn regarding the depend- 
ence of the fluorescent “ function” upon the molecular constitu- 
tion of the ammonium salts may be best appreciated through an 
€xamination of the constitutional formule of the organic acids 
whose salts were employed. The list is arranged, as far as possi- 
ble, in order of fluorescigenic value. 
Asparagin, COOH. CH,. CH. (NH;). CONH3. 
Succinic acid, COOH. CH,. CH,. COOH. 
Lactic acid, CH;. CHOH. COOH. 
Citric acid, COOH. C(OH). (CH,COOH)s. 
Tartaric acid, COOH. CHOH. CHOH. COOH. 
te er ae re 
Uric acid, Nit.CO, NH. CO,C=C.NH. CO-NH. 
l j 
Acetic acid, CH,. COOH. 
Oxalic acid, COOH. COOH. 
Formic acid, H. COOH. 
Lepierre,” who studied the behavior of a species closely 
related to if not identical with B. fi. putridus, draws from his 
work the far-reaching conclusions that the fluorescence is inti- 
mately bound up with: first, the bibasicity of the acid ; second, 
the existence in the molecule of at least two groups of CH,. 
Conclusions analogous to these cannot be deduced from my own 
* Ann. de I’Inst. Pasteur 9: 643. 
