2 SELMAN A. WAKSMAN 



no free nitrogen given off; no reduction of nitrates to ammonia 

 could be demonstrated. Krainsky (1914) stated that the actin- 

 omycetes assimilate both organic and inorganic nitrogen; of the 

 organic substances, the proteins and amino bodies could serve 

 not only as sources of nitrogen, but also of carbon; casein and 

 peptone were split by all species to ammonia. All species, with 

 one exception, grew readily upon a solution of gelatin in water 

 (with the addition of 0.05 per cent K 2 HP0 4 ), A. flavochromogenus 

 forming an insoluble gelatin compound. The actinomycetes 

 assimilated ammonia, nitrite and nitrate nitrogen compounds; 

 NH 4 C1 was not always favorable, particularly in the presence of 

 glucose. Nitrates were reduced to nitrites by most actino- 

 mycetes, this varying with the composition of the medium; 

 with many species, the nitrite formation was absent, due to the 

 fact that this phenomenon is so slow that all the nitrites formed 

 are at once assimilated by the cells; in no instance could am- 

 monia be demonstrated as a reduction product of nitrates and 

 nitrites; A. flavus alone could not reduce nitrates. No urease 

 could be demonstrated, while casein was split by means of a 

 proteolytic enzyme. 



Emerson (1917) stated that since Actinomyces colonies were 

 formed on nitrogen free media, these organisms are able to assim- 

 ilate free nitrogen. This last fact could in no instance be con- 

 firmed by the writer. The development of Actinomyces colonies 

 on nitrogen-free agar media is due to the fact that many of these 

 organisms can develop readily with mere traces of nitrogen, 

 which are probably present as impurities in the agar or as traces 

 in the laboratory air. 



Waksman and Curtis (1916) found that nearly all the actino- 

 mycetes studied could liquefy gelatin, varying in degree of 

 rapidity of liquefaction, but they were found to be rather weak 

 as ammonifying organisms. Lutman and Cunningham (1914) 

 have shown that the ammonia production of A. scabies is small 

 compared with that of bacteria under similar circumstances. 



