Mar. 24, 1919 Ammonification of Manure in Soil 345 



into two groups, one ^ producing no acid and the other (containing the 

 majority of the strains) producing acid from dextrose and sucrose but 

 not from lactose or glycerin. There proved to be some irregularity upon 

 repetition of the test, but not a great deal. It was then felt that the 

 difference between these two groups of strains might be that one pro- 

 duced more alkalinity from the peptone than the other and that its 

 acid production was thus obscured. The test was therefore repeated a 

 few times on a tartrate agar ^ in which Ps. cavdatus was found to cause 

 no change in reaction unless some sugar were present. With this medium 

 more consistency was observed upon repetition of the test, but the dif- 

 ference between the two groups was still sharp. The acid group acidified 

 lactose in this medium as well as dextrose and sucrose. It is therefore 

 concluded that typical Ps. caudatus produces acid from dextrose, sucrose, 

 and lactose, but not from glycerin, its acid production from lactose being 

 too weak to neutralize the alkalinity produced from the peptone if grow- 

 ing in ordinary media. The nonacid strains, with the exception of the 

 nonchromogenic one, died while under cultivation in the laboratory; so 

 it is felt that their failure to produce acid may have been the first evi- 

 dence of loss of vigor. Hence, they are not considered to be distinct 

 from the typical acid formers. The strain used by Bright in the experi- 

 ments reported above was a vigorous acid producer. 



Nitrate reduction. — Irregular results were obtained with this test 

 also. Ordinary nitrate broth proved so unsatisfactory that tests were 

 made on agar slants as described for Ps. fliwrescens (p. 341). On beef- 

 extract peptone agar, the acid group of strains, above mentioned, showed 

 a strong nitrite reaction; the nonacid group, with the exception of the 

 nonchromogenic strain, showed no nitrite; the nonchromogenic strain 

 when first tested was distinctly nitrite-positive, but after a few months 

 all three substrains of this organism were found to have lost their nitrite- 

 producing power. To investigate this matter further, the synthetic 

 sucrose-nitrite agar ^ already used for Ps. fluorescens was employed. 

 On this agar an occasional culture was found to produce nitrite that had 

 showed no nitrite reaction on the nitrate-peptone agar, and ammonia was 

 observed in almost all cases. Growth was very poor, however, with the 

 nonacid group of strains. Inasmuch as there was no possible source of 

 ammonia in this medium except the nitrate, the conclusion was drawn 

 that Ps. caudatus reduces nitrate to nitrite and ammonia, but that some 

 cultures convert the nitrite into ammonia so rapidly that a nitrite test is 

 generally negative. The presence or absence of the nitrite test depends 

 upon the relative rate of these two processes, which is probably associated 

 with the vigor of the culture. Hence, the failure of the nitrite test is no 



proof that any particular culture is not Ps. caudatus. 

 ? . 



1 One of the strains in this group was the one that had lost its pigment-producing power. 

 ^ Formula given in footnote, p. 340. 



' Formula given in footnote, p. 341 . Sucrose (not dextrose) was used in this formula because of the pres- 

 ence of ammoniacal impurities in the dextrose on hand. 



