302 PRINCIPLES OF SOIL MICROBIOLOGY 



ing the medium to become acid. No acids are formed from carbohy- 

 drates. Certain actinomyces will grow in media containing 12 per cent 

 glycerol or 7 per cent NaCl. 48 In the presence of 18 per cent glycerol 

 and 9 per cent NaCl, no growth was observed. Actinomyces were 

 found 49 to grow in the presence of 5 per cent of KC1, NaCl, KN0 3 , 

 NaN0 3 , as well as mixtures of these, but spore formation is depressed. 

 Ten per cent of the salts repressed the growth of all forms except one. 

 Magnesium salts proved much more injurious. Small quantities of 

 alkali earths stimulated, while larger quantities injured growth and 

 spore formation. Difficultly soluble carbonates have little effect. 

 AgN0 3 inhibited growth completely; 0.1 per cent Cu as CuS0 4 or 

 CuCl 2 was injurious, HgClo was less injurious. Lead nitrate and iron 

 salts were least injurious. Lieske could not observe any diminution in 

 growth of various actinomyces when 15 per cent cane sugar was added 

 to nutrient bouillon. Slight growth was obtained in the presence of 

 20 per cent cane sugar; no further growth was observed in the presence 

 of 30 per cent sugar. Actinomyces are found abundantly in nature on 

 substances containing very little water and are very active in the soil in 

 dry seasons. 



Influence of poisons. The addition of benzol to the soil was found to 

 stimulate the development of actinomyces but they are injured by the 

 application of carbon bisulfide. 50 These organisms are not very sensi- 

 tive towards chemical poisons but cannot resist the action of metallic 

 salts. The limit of the action of a poison can be changed by gradual 

 adaptation. Of the dyes, methylene blue, methyl violet and gentian 

 violet are most toxic, preventing growth in 1:500,000 dilution in nutri- 

 ent bouillon. 27 



Reduction of nitrates and other compounds. The majority of actino- 

 myces species are able to reduce nitrates to nitrites, but not to ammonia 

 nor to atmospheric nitrogen. 51 By using the ordinary Czapek's solution, 

 nitrite formation can be demonstrated to run parallel to the growth of 

 the organism. Some starch solution and 0.5 per cent KN0 3 may be 

 added to ordinary nutrient agar, which is then placed in Petri dishes, 



48 Neukirch, 1902 (p. 293). 



49 Miinter, F. tJber den Einflusz anorganischer Salze auf das Wachstum der 

 Aktinomyceten. Centrbl. Bakt. II, 44: 673-695. 1916. 



60 Stormer, K. tlber die Wirkung des Schwefelkohlenstoffs und ahnlicher 

 Stoffe auf den Boden. Centrbl. Bakt. II, 20: 282-286. 1908. 



51 Fousek, A. Die Streptothricheen und ihre Bedeutung in der Natur. Mitt, 

 landw. Lehrkanz. K. K. Hochsch. Bodenk. Vienna, 1: 217-244. 1912. 



