5^2 Journal of Agricultural Research voi. iv. no. 6 



ments it was found that the development of the different types of pro- 

 tozoa varied greatly with the culture solutions employed in studying 

 these organisms. 



The purpose of this problem was to study : 



(i) The development of protozoa in different culture solutions. 



(2) The development of protozoa from varying amounts of soil inocu- 

 lations. 



(3) The comparison of the numbers and types of protozoa developed 

 from compost and field soils. 



A large sample of the same 20 per cent compost greenhouse soil con- 

 taining 24.30 per cent of moisture which was used in the work on green- 

 house soils in Part II was collected from a bin in the greenhouse. Like- 

 wise a sample of a heavy clay field soil which had not received fertilizer 

 for several years was collected from a young orchard. This soil, which 

 was taken 3 inches from the surface, had a moisture content of 18.35 

 per cent, and the temperature at the time of collection was 0.5° C. To 

 100 c. c. portions of 3 per cent dried-blood extract with 0.05 per cent 

 of dibasic potassium phosphate and the same amount of a 10 per cent hay 

 infusion ^ were inoculated with i, 5, 20, 50, and loo gm. portions of each 

 soil. The inoculated solutions were examined for protozoa and then 

 incubated at 22° C. for a period of 30 days. At the same hour each day 

 counts were made of the organisms developed. The examinations were 

 made under the low power of the microscope and the organisms enumer- 

 ated by the improved loop method as described in Part I of this paper. 

 When the specially prepared slide was not used, in counting culture 

 solutions containing more than 350,000 organisms per cubic centimeter 

 the loop of culture solution was transferred to a plain glass slide, a 5 mm. 

 square of which was carefully ruled off into 40 to 50 small fields of equal 

 size. All the organisms in the incomplete fields on the outer portions of 

 the film of culture solution were counted, the average of the numbers in 

 several fields were taken, and the numbers of organisms calculated as 

 in the improved loop method. This method checked very closely with 

 counts made by means of the special slide. 



As in the previous work, the same difficulty of distinguishing large bac- 

 teria from small flagellates was encountered. Hence, to facilitate the 

 enumeration of the organisms it was thought advisable to make all of 

 the counts under the low power of the microscope. In many cases it 

 was difficult to distinguish small ciliates from flagellates; hence, notwith- 

 standing precautions taken in enumerating the organisms, it is quite 

 probable that some small ciliates might have been counted as flagellates, 

 and vice versa. 



1 This formula was recwmmended by N. Kopeloff, H. Clay Lint, and David A. Coleman in 1915, in an 

 unpublished manuscript entitled, " A New Method for the Counting of Protozoa and Some Media for Their 

 Development." 



