Le — 
1899 | PRODUCTION OF FLUORESCENT PIGMENT 29 
0.2 per cent. asparagin, O0.0O0OI per cent. sodium sulfate, and, 
respectively, I, 0.5, 0.2, 0.1 per cent. neutral sodium phosphate, 
B. fl. albus develops pigment most rapidly and intensely in the 0.1 
per cent. phosphate solution. JB. /7. putridus and B. fi. tenuis, on the 
other hand, develop pigment soonest in the I per cent. phosphate 
solution, and the former species does not develop any at all in 
the solutions with slighter phosphate content. As arule, how- 
ever, especially in solutions containing a larger amount of sul- 
fate, a phosphate content as high as I per cent. interferes 
with the production of fluorescent pigment and the culture 
generally assumes a muddy yellow tint. The same thing occurs 
if a considerable quantity of ammonium salt be employed. 
B. ft. albus, for example, in a solution of 2 per cent. of ammo- 
nium tartrate and the usual quantities of phosphate and sul- 
fate, imparts less of a fluorescent tinge and more of a yellow 
color to the medium, than with the ordinary 0.5 per cent. tartrate 
solution. This fact is of interest in connection with Lepierre’s 
conclusions,” which are based upon experiments made with 2 
per cent. solutions of ammonium salts. The high acidity of 
such strong solutions as he employed, however, was probably an 
even greater factor in the vitiation of his results than the simple 
concentration of the medium. 
INFLUENCE OF LIGHT UPON PIGMENT PRODUCTION. 
Pigment production is perceptibly affected by light. I have 
made no experiments with regard to the action of direct sunlight, 
but have confined myself to a comparison of cultures kept in 
the dark with others kept in diffuse daylight. The latter cultures 
were kept on a desk near the windows of a room into which no 
direct sunlight, but only north light entered; the former were 
kept in a locker in the same room and as nearly as possible at 
the same temperature, although variations of from three to four 
degrees were occasionally observed. These slight temperature 
variations were, however, sometimes on one side, sometimes on 
the other, and I have seen no reason to infer that the course of 
*? Ann. de I’Inst. Past. 9 : 643. 1895. 
