22 BOTANICAL GAZETTE [JANUARY 
nience, however, refer to the cultures by the names they bear 
just as if they were so many distinct ‘‘species.” 
The methods employed have been selected with a view to 
obtaining constancy and uniformity of conditions. Owing to the 
familiar fact that the different commercial peptones vary widely 
in chemical composition and nutritive value, and since Gessard™ 
and Lepierre* have definitely proved that the production of 
fluorescence by certain bacteria is profoundly affected by the 
nature of the peptone used, I have carried out my investigations 
with the aid of simple solutions of chemical compounds whose 
molecular composition and arrangement are more accurately 
known. The nitrogenous basis of these nutrient media has con- 
sisted of asparagin or ammonium salts, and to these have been 
added other substances according to the nature of the experi- 
ment. The utmost care has been taken to obtain chemicals of 
_ strict purity, since a mere trace of foreign substance is in some 
cases sufficient to vitiate the result. 
In all of my solutions I have employed water redistilled in 
glass. The various flasks and test-tubes used in my experi- 
ments have been thoroughly cleansed with chromic acid clean- 
ing mixture which has been very carefully washed out and 
the vessels finally rinsed in distilled water. A suitable quantity 
(usually 7-8°°) of the nutrient solution has been placed in thin- 
walled test-tubes and sterilized in the steam-bath by the discon- 
tinuous method. Prolonged heating and the use of the autoclave | 
have been avoided as they have been found to affect the consti- 
tution of some of the media. 
Inoculation of the media has usually been made from vigor- 
ous agar growths about three to five days old, but I have also 
often used for this purpose fluid media in which abundant pro- 
duction of pigment had occurred, e. g., an asparagin-phosphate- 
sulfate solution, but without noting any difference in the outcome. 
The cultures have always been kept in the dark and at the 
room-temperature, 18—20°C., except when specified otherwise. 
Ann. de l’Inst. Past. 6: 8or. 1892. 
* Ann. de I’Inst. Past. 9: 643. 1895. 
