129 



TESTS FOR NITRITES. 



PKrroNl/Kl) ]^)KKK l^HOTHS. 



Tw(^ stocks were used: (1) A strongly alkaline beef l)roth (stock 

 3S'2) with addition of 1 per cent Witte's peptonum siccum; (2) a 

 slightly alkaline beef broth deprived of its nui.-cle sugar b}^ growing 

 £. coli in it for 17 hours in the thermostat. This latter was clarified 

 with the whites of 4 eggs, which were neutralized by HCl, and for- 

 tified with 2 per cent Witte's peptone. These cultures were tested on 

 the twenty-second da}' after good growth. Neither gave any nitrite 

 reaction with the indol-sulphuric acid test, the indol being that nor- 

 mally present in the cultures. 



Peitoxized Usciiinsky'.s Solution. 



This stock consisted of Uschinsky's solution with the addition of 1 

 per cent Witte's peptone. The tests were made at the end of 22 days. 

 There was no nitrite reaction with the indol-sulphuric acid test, the 

 indol being that normally present in the cultures. 



2siTRATE Bouillon (Stock 474). 



This consisted of— 



Distilled water, 1,000.0. 



Witte's peptone, 10.0. 



Beef extract, 2.5. 



Chemically pure potassium nitrate, 3.0. 



and sodium hydrate sufiicient to render the fluid +10 of Fuller's scale. 



Ps. hyacinthi grew readily in this medium without gas production. 

 Examinations for nitrite were made on the sixth, sixteenth, and 

 twentieth da3's, using the iodine-starch test — i. e., to each tube was 

 added 1 c. c. of thin boiled starch water, 1 c. c. of one-half per cent 

 potassium-iodide water (which should be freshly prepared), and finally 

 a few drops of a fluid consisting of 2 parts of c. p. sulphuric acid and 

 1 part of distilled water. Xo trace of nitrite reaction could be 

 obtained with this reagent. Subsequenth' grape sugar was added to 

 some tubes of this nitrate bouillon (100 milligrams per 10 c. c), but 

 even in the presence of this agent 7i-. hyacintld was unable to reduce 

 any nitrate to nitrite (8 days). Tubes of Bacillus coli and of Bacillus 

 carotovorus were used for comparison. These became blue-black, like 

 ink, on addition of the sulphuric acid. 



Ps. campestris and Ps. stewarti resemble Ps. hyacinthi. Neither one 

 is able to reduce potassium nitrate to nitrite in peptonized bouillon 

 cultures, either with or without grape sugar. Comparisons were also 

 made with Bacillus amylovorus and B. pyocyaneus pevicarditidis. The 

 former does not reduce nitrates to nitrites. The latter (like various 

 217SS— No. 28-01 9 



