Sept. 15, 191S ' Soil Protozoa 543 



A sample of the 20 per cent compost greenhouse soil which had been 

 used in previous experiments was collected. Likewise another sample 

 of the heavy unfertilized clay soil used in another study was brought to 

 the laboratory. A third sample, a light loamy soil which contained 12.19 

 per cent of* moisture and which had received an application of 20 tons of 

 barnyard manure per acre for the last 20 years, was collected 3 inches 

 below the surface. The upper i^ inches were frozen, but the tempera- 

 ture at 3 inches was 1.5° C. at the time of sampling. 



Four 200 c. c. Jena Erlenmeyer flasks containing 100 c. c. portions 

 each of 3 per cent dried-blood extract with 0.05 per cent of dibasic potas- 

 sium phosphate and the same number of flasks containing 100 c. c. por- 

 tions of a 10 per cent hay infusion were inoculated with 5-gm. samples of 

 the newly collected moist soils. (It was found in Parts II and III that 

 on the gram basis a greater development of protozoa can be produced 

 with smaller amounts of soil.) The inoculated solutions were examined 

 for living protozoa, and then one flask of each solution of hay infusion and 

 blood extract inoculated with each soil was incubated at temperatures 

 of 5 to 7° C, another set at 15 to 16° C, a third at 22 to 23° C, and a 

 fourth at 29 to 30° C, for a period of 30 days. At the same hour each 

 day these solutions were examined and the living protozoa counted by 

 the improved loop method under the low power of the microscope. 



In order that the inoculated solutions should not vary in temperature 

 during examination, they were kept in constant-temperature baths. In 

 like manner, to guard against excessive evaporation from the solutions 

 inoculated at 29 to 30° C, each flask was placed in a container of water 

 and covered with a large beaker. To prevent variation through the 

 possible effect of excessive light, the flasks were screened in all cases 

 during the incubation period. 



As in the previous experiments, the classification of protozoa that was 

 followed in this problem was as follows: The small ciliates included all 

 organisms from the smallest to and including Colpidium colpoda. The 

 vorticella type were also included. The large ciliates included all forms 

 larger than Colpidium colpoda. The flagellates included all the forms 

 of flagellates that were observed. 



DEVELOPMENT OF SOIL PROTOZOA IN CULTURE SOLUTIONS AT VARIOUS 



TEMPERATURES 



DEVELOPMENT OF SMALL CILIATES 



That the varying condition of temperature is a very important factor 

 in the development of soil protozoa in culture solutions is noted by the 

 marked variation in the numbers of organisms present. For the devel- 

 opment of small ciliates a temperature of 6 to 7° C. proved very unfavor- 

 able, as in none of the inoculated solutions did the organisms exceed 

 265,000 per gram. At this temperature blood extract seemed to be more 

 97209°— 15 5 



