SOIL PROTOZOA 319 



of 2 mm. favored the growth of protozoa. Meat extract agar may also be used. 

 Bacterial growth takes place from those cells which are transferred with the 

 protozoa. In some cases, special bacterial cultures are inoculated. To pre- 

 vent the accumulation of injurious by-products, the protozoan culture must be 

 frequently transferred. A rapid development of bacteria may lead to the de- 

 struction of protozoa or may prevent their growth. 27 Media containing 0.3 to 

 0.5 gram Liebig's beef extract, 0.3 to 0.5 gram NaCl and 20 grams of agar in 1000 

 cc. of water have commonly been employed. Beijerinck 28 used yeasts for the 

 cultivation of amoebae and ciliates. As a solid medium for the cultivation of 

 amoebae, a mixture of 20 parts of agar, 100 parts of beef bouillon and 900 parts 

 distilled water of a neutral or slightly alkaline reaction may be employed. 29 



The use of dead bacteria for the cultivation of amoebae has been sug- 

 gested. 30 Amoebae and ciliates were found 31 capable of assimilating pure 

 cultures of bacteria, utilizing dead cells as well as small particles of 

 protein material. Gram negative bacteria were preferred to gram-posi- 

 tive forms; young bacterial cultures in many cases were more assim- 

 ilable than old cells. Successful cultures were obtained on bacteria 

 smeared on the plate, then autoclaved at 130°, for 1 hour. Azo- 

 tobacter was found 32 to offer good food for amoebae, on a medium 

 containing 10 grams of dextrin, 2 grams K 2 HP0 4 , 0.2 gram MgS04, 

 0.2 gram CaC0 3 , 10 grams agar in 1000 cc. water. Paramoecium was 

 also grown in pure cultures of bacteria. 33 Severtzoff 34 cultivated an 

 amoeba on a pure culture of Bad. coli; she found that the bacterium was 

 destroyed by a small quantity of chlorine, while the protozoan cysts 



27 Oehler, R. Wirkungen von Bakteriengiften auf Ciliaten. Centrbl. Bakt. 

 I, Orig., 86: 494-500. 1921. 



28 Beijerinck, M. W. Kulturversuche mit Amoben auf festem Substrat. 

 Centrbl. Bakt. I, 19: 257-267. 1896; 21: 101-102. 1878. See also Mouton, 

 1902 (p. 316). 



29 Wasielewski, T. V., and Kiihn. Untersuchungen iiber Bau und Teilung des 

 Amobenkerns. Zool. Jahrb. Anat., 38: 253. 1914, also Heidelberg. Akad. Wiss 

 Math. u. Naturw., 1: 1-31. 1913. 



30 Tsujitani, J. Uber die Reinkultur der Amoebae. Centrbl. Bakt. I, 24: 

 666-670. 1898. 



31 Oehler, R. Amobenzucht auf reinem Boden. Arch. Protistenk., 37: 175- 

 190. 1916; Flagellaten und Ziliatenzucht auf reinem Boden. Ibid., 40: 16. 

 1919; 41: 34. 1920; 49: 112-134. 1924; Gozony, L. Kultur von Flagellaten in 

 festen Nahrboden. Centrbl. Bakt. I, Orig., 84: 565-566. 1920. 



32 Welch, M. W. The growth of amoeba on a solid medium for class use. 

 Trans. Amer. Micr. Soc, 36: 21-25. 1917. 



33 Hargitt, F. T., and Fray, W. W. Paramoecium grown in pure cultures of 

 bacteria. Anat. Rec, Philadelphia, 11: 516. 1916; Jour. Exp. Zool., 22: 421. 

 1917. 



34 Severtzoff, 1924. 



