340 Journal of Agricultural Research voi. xvi. No. 12 



production by titration, the latter writers titrating hot, a procedure 

 which Clark (j) has shown to be illogical. Tanner finds acid production 

 only in dextrose, while Edson and Carpenter find it common with the 

 other sugars, undoubtedly because the H-ion concentration is increased 

 by heating the culture previous to titrating. 



Blanchetiere (i) avoids this error by using litmus agar. He finds 

 acid produced from dextrose and levulose, but not from the disaccha- 

 rids; but as levulose is a difficult sugar to purify, and as Blanchetiere 

 says nothing about the source of his sample, he leaves some doubt in 

 the reader's mind as to whether it was actually free from dextrose. He 

 distinctly states that lack of acid reaction in this medium does not 

 mean failure to produce acid, but simply that not enough acid is pro- 

 duced to neutralize the ammonia formed from the peptone. This shows 

 Blanchetiere realizes another source of error, but feels unable to over- 

 come it. Plainly, with these two sources of error, the data in the litera- 

 ture as to acid production by fluorescent organism are not reliable. 



In the present work Blanchetiere's technic has been modified by 

 using bromcresol purple in place of litmus as an indicator. The result 

 has been in practically every case to find acid produced from dextrose 

 and sucrose, but not from lactose and glycerin. The strain studied in 

 Bright's experiments, above reported, showed these reactions very 

 constantly. A synthetic medium containing ammonium tartrate as 

 its only source of nitrogen ^ was then used in an attempt to overcome 

 the error resulting from the presence of peptone in ordinary agar, and 

 somewhat different results were obtained. Even with this method there 

 was no agreement in the results obtained with the different fluorescent 

 organisms. The strain used by Bright showed acidity from dextrose 

 and sucrose, the latter reaction disappearing after the first day; while 

 another strain agreeing with it in every respect showed strong and per- 

 sistent acidity in sucrose as well as dextrose. The conclusion was reached 

 that Ps. fluorescens produces acid from both dextrose and sucrose, but 

 that with the latter sugar the acid production is likely to be obscured by 

 other activities tending to lower the reaction of the medium. 



Reduction of nitrate." — The literature is full of conflicting data in 

 regard to the action of fluorescent bacteria on nitrate. There are several 

 different possibilities: (i) Reduction to nitrite; (2) reduction to nitrite, 

 then to ammonia; (3) reduction to ammonia without appreciable accumu- 

 lation of nitrite; (4) reduction to free nitrogen — namely, denitrifica- 

 tion; (5) assimilation of the nitrogen of the nitrate, with or without 

 prex-ious reduction. It has not proved possible to devise a simple test 

 to distinguish with certainty between these five different possibilities, 

 hence, the confusion. 



' The formula of this rnedium was: Distilled water, i.ooo cc; agar, is cin.; calcium chlorid (CaChX 0.5 

 gm ; potassiura phosphate (KcHPOi), 0.5 cm.; ammoniuxn tartrate [(NH4)2CiH.i06a], 10 gm.; with 10 gm.; 

 of the sugar (or glycerin) under investigation. 



