SOIL ACTINOMYCES 301 



and found that he could obtain a pure culture of the organism from the 

 dry material after preserving it for ten years. Lieske found that only 

 the saprophytic spores and mycelium were viable after they had been 

 preserved on filter paper in a desiccator for eighteen months. This 

 would point to the fact that the pathogenic actinomyces are not carried 

 over for any long time in dry soil or straw, as is often assumed. 



Direct sunlight does not exert any injurious effect upon the actino- 

 myces and does not modify their growth. Exposure to ultraviolet 

 rays for 10 minutes does not affect them; after one hour, the organism is 

 definitely affected but not destroyed. Rontgen rays have no influence. 27 



Influence of reaction and salt concentration. It has been generally 

 observed that alkalies and alkali substances favor the development of 

 actinomyces, while acids and acid substances injure their activities. 

 This is particularly true of inorganic acids, since the organic acids are 

 utilized to some extent by the organisms and are thus broken down. 

 The limiting acid reaction for the majority of soil actinomyces is pH 

 4.8 to 5.0, although some species may grow at as high an acidity as 

 pH 3.0 to 4.0. The optimum is pH 7.0 to 8.5. On the alkaline side, 

 the majority of organisms will still grow at pH 8.6 to 9.0, while 

 some will grow even at more alkaline reactions. This fact can be uti- 

 lized in adjusting the reaction of the soil so as to prevent the develop- 

 ment of A. scabies causing potato scab. 



Gillespie 45 was the first to point out the fact that soils having a reac- 

 tion of pH 4.8 or less are free from scab, while those having a reaction 

 more alkaline than pH 4.8 are apt to have scab. Various strains of A. 

 scabies may behave somewhat differently: some may be inhibited in 

 their development at pH 5.0, while others only at pH 4.6. The organ- 

 isms are also able to withstand a somewhat greater acidity in the soil 

 than in solution. 46 The reaction of the medium is usually changed by 

 the growing organism to less acid or more alkaline ; 47 this is true of media 

 containing proteins, amino acids and NaN0 3 . The proteins and amino 

 acid are decomposed with abundant formation of ammonia. With 

 ammonium salts, the ammonium radical is rapidly used up, thus allow- 



45 Gillespie, L. J. The growth of the potato scab organism at various hydro- 

 gen-ion concentrations as related to the comparative freedom of acid soils from 

 the potato scab. Phytopath., 8: 257-269. 1918. 



46 Waksman, S. A. The influence of reaction upon the growth of actinomyces 

 causing potato scab. Soil Sci., 14: 61-79. 1922. 



47 Naslund, C. f and Dernby, K. G. Untersuchungen iiber einige physiolo- 

 gische Eigenschaften der Strahlenpilze. Biochem. Ztschr., 138: 477. 1923. 



