Sept. 15, I9IS Soil Protozoa 555 



larger numbers of organisms would develop from this quantity than 

 from larger amounts of soil. 



In comparing the development of protozoa from moist and dry soils 

 (Part II) very little difference in the development of small ciliates, large 

 ciliates, and flagellates was found, but in order that the conditions of 

 the soil protozoa would not be varied in this experiment moist soil was 

 used. 



Cunningham (3, p. 14) found 22° C. the optimum temperature for the 

 development of most soil protozoa. In this problem a great variation 

 was found. The greatest uniformity of results in the development of 

 small ciliates was obtained at 15° to 16°. With flagellates 6° to 7° was 

 the optimum in some solutions and 15° to 16° in others. As compared 

 with the development at 22° to 23°, a much longer period of time was 

 required for the maxinmm numbers of protozoa to develop at the tem- 

 peratures lower than 22° to 23°. It may be added that 22° is more con- 

 venient to maintain in the laboratory. 



In culture solutions the conditions are much different compared to 

 those found in the soil, as was already suggested by Martin (12). Of the 

 solutions examined the hay infusion proved the most satisfactory for the 

 development of large numbers of organisms, the total being much greater 

 than those appearing in the natural soil. It is probable that the results 

 produced by adding the soil to tap water more nearly represents the 

 conditions as they are found in the soil. 



In order that the results may be comparable, the examinations of the 

 inoculated culture must be made periodically every day. The length of 

 time a culture should be incubated will vary with the temperature of 

 incubation, kind and amount of soil, and kind of medium. Under cer- 

 tain conditions some types of protozoa appear on the first day after 

 inoculation; these would multiply very rapidly and probably depress 

 the development of other forms. Again, certain types might not appear 

 until the eighteenth or twenty-second day after inoculation. With few 

 exceptions, however, at temperatures of 15°, 22°, and 29° C, the maxi- 

 mum development of small ciliates and flagellates in the culture solu- 

 tions inoculated with the soils examined was not reached until the thir- 

 teenth or fourteenth day. The writer is of the opinion that the develop- 

 ment in artificial culture solutions in the first five to seven days would 

 more nearly show the numbers of cysts of small ciliates and flagellates 

 present in the soil. 



The conditions under which the experiments have been carried out 

 seemed to have been very unfavorable for the development of large ciliates 

 and amoebae. In the soils examined, however, cysts of large ciliates 

 could be readily seen under the microscope. Cauda and Sangiorgi 

 (2, p. 396) developed many amoebae in Giltay's, Omelianski's, Hiltner's, 

 peptone, and mannite solutions, showing that these organisms were pres- 

 ent in the soils which they examined. 



