M [CRO-ORGANISMS OF MAPLE SAP 



3. . Iction on nitrates in nitrate broth. — Medium : 



Water 1 ■ cc. 



Peptone ( Witte's) L. gr. 



Potassium nitrate, c. p -• 



The cultures were tested for nitrites by the iodo-starch reaction 



as follows [i~ :<>$). A starch paste was made by boiling a 4' ', 



aqueous mixture of potato starch; to the 10 cc. of culture ! cc. 



of the starch paste and 1 cc. of freshly prepared potasium iodid 



water (0.4' < 1 were added, followed by three drops of sulphuric 



acid (2 parts c. p. sulphuric acid to 1 part water). One series 



of cultures and controls was tested upon the second, fifth, and 



ninth da) s. 



A diphenylamine reagent was prepared as follow- (32:340) : 

 5 grams of diphenylamine were dissolved in 100 cc. of pure con- 

 centrated sulphuric acid and added to 20 cc. of water, hi case 

 of negative nitrite tests with the iodo-starch reaction, a few drops 

 of diphenylamine reagent were poured down the side of the tube 

 in such a manner as to form 2 layers. A blue contact zone in- 

 dicated the presence of nitrates. When a positive nitrite reaction 

 was observed the nitrate test was performed with another cul- 

 ture. 



Second day. — A positive nitrite reaction (immediate black- 

 ening) was given by Ps. mesenteriea, XXXVI, and Id. Nitrates 

 were present in all by the diphenylamine reaction. Ammonia 

 was indicated in all except CXV by Nessler's reagent. 



Fifth day. — An immediate reaction for nitrites was given b) 

 Ps. mesenteriea. XXXVI, and LI. Nitrates and ammonia were 

 indicated in all. 



Ninth day. — Immediate positive reaction for nitrites occurred 

 in cultures of Ps. mesenteriea. XXXVI, and LI and Ps. fluo- 

 rescens showed traces. Nitrates were indicated in all. A posi- 

 tive reaction for ammonia was obtained from all culture-, espe- 

 cially strong in Ps. putrida and CXLVIII. 



A nitrate medium in which tap water was substituted for 

 distilled water was employed in fermentation tube-. The tests 

 were conducted as before, about 10 cc. of the medium being 

 poured into clean test tubes, for this purpose. 



