12 SELMAN A. WAKSMAN 



amino acids. The particular thing to call attention to in this 

 respect is the reduction of nitrates to nitrites, which is greatly 

 influenced by the source of carbon. Out of 45 species, 35 reduced 

 nitrates in the presence of starch and only 20 in the presence of 

 sucrose. Nitrite reactions were obtained in certain cases even 

 when the proteins and amino acids were used as sources of nitro- 

 gen. Notably a strain of A. calif omicus, when freshly isolated 

 from the soil, produced nitrites not only from proteins but also 

 from ammonium sulfate. This fact recalls a paper by Joshi 

 (1915), who reported a bacterium which could transform protein 

 nitrogen directly into nitrites, without the nitrogenous sub- 

 stances undergoing the 3 stages of splitting of proteins to am- 

 monia by one or more groups of organisms, and oxidation of 

 ammonia to nitrites, then to nitrates by Nitrosomonas and 

 Nitrobacter respectively. The photograph of the organism as 

 well as its action strongly resemble that of an Actinomyces. 

 This ability of the actinomycetes to produce nitrites out of 

 nitrates, without any further reduction of the nitrogen com- 

 pounds to ammonia or elementary nitrogen, was pointed out by 

 Beijerinck (1900), Fousek (1912) and Krainsky (1914). The 

 latter used plate cultures only and found that few species were 

 able to reduce nitrates to nitrites strongly; in many cases the 

 small quantities of nitrites produced were assimilated by the 

 organism as soon as formed. The data on the reduction of 

 nitrates to nitrites, affected by the source of carbon were re- 

 ported in a previous paper and are summarized in table 2 for the 

 purpose of comparison. 



The nitrites were determined by the Griesz (1870) colorimetric 

 method. First 1 cc. of sulfanilic acid solution and 1 cc. of 

 a-Napthylamin solution were mixed in test tubes and allowed 

 to stand a few minutes, so as to insure against the presence of 

 any nitrites in the tubes. Then 1 cc. of the culture was added 

 to the tube, shaken, the mixture allowed to stand in the cold 

 three to four minutes and a reading taken. The active nitrate 

 reducing organisms, such as A. violaceus-ruber, reduce with all 

 sources of carbon; some that do not reduce nitrates readily, such 

 as A. violaceus-caesari, A. albus, and A. bobili produce no nitrites 



