34 BOTANICAL GAZETTE [ JANUARY 
work. The difference between acetic acid on the one hand and 
oxalic and formic acids on the other is certainly significant, but 
that neither the carboxyl (COOH) nor the methylene (CH,) 
grouping is essential to pigment production is shown by the avail- 
ability of urate. The difference between tartrate and succinate, 
as well as that between formate and acetate does, however, 
clearly indicate that, other things being equal, the presence of 
the methyl or methylene group is coincident with superior nutti- 
tive value and fluorescigenic power. 
4. The presence of acid in the medium not merely conceals 
the existence of the substance to which the color is due, but 
interferes with those vital activities of the bacilli which, in an 
alkaline solution, lead to the production of that substante. 
5. Diffuse daylight is unfavorable to pigment production. 
6. If chemical substances that prove, when in certain pro- 
portions, favorable to growth and to the production of pigment 
be present in excess of a certain quantity, the production of pig- 
ment will be checked, although growth may be more abundant 
than before. 
I may add, as an obiter dictum, that since the pigment is 
of no discoverable advantage to the organisms possessing the 
power of producing it, its production is probably purely inci- 
dental and not an essential vital act. The “ fluorescigenic func- 
tion,” upon which some bacteriologists dwell, is in my opinion 
simply the expression of certain changes wrought by the organ- 
ism upon the nutrient substratum in which it lives. When the 
substratum contains certain compounds, the metabolic activities | 
of the organism adjust themselves to these conditions and the 
metabolic products differ correspondingly. It is purely a mat- 
ter of accident and of no physiological significance that under 
certain conditions one of these metabolic products happens to 
be fluorescent. 
THE UNIVERSITY oF CHICAGO, 
