Dec. 13, 191S Activity of Soil Protozoa 479 



In order to determine the presence of motile protozoa in the soil, the 

 writer has found the direct method of examining the soil to which a little 

 water has been added the most satisfactory. 



Several drops of sterile tap water (15 pounds' pressure for 15 minutes) 

 are placed on a clean slide; then by means of a stirring rod a small por- 

 tion of soil is stirred in this water and spread out in a thin film, so that 

 the observer can readily see between the soil particles. Examinations 

 are then quickly made under the low power (16 mm. lens) of the micro- 

 scope.^ As soon as the soil touches the water, the time is recorded 

 and the examination is continued for a period of not more than two 

 minutes, in this way reducing the possibility of error which the observer 

 might make on account of the rapid excystment of the protozoa, as was 

 suggested above. 



PROTOZOAN ACTIVITY IN SOILS OF DIFFERENT MOISTURE CONTENT 

 AND UNDER CONSTANT AND VARIABLE TEMPERATURES 



GREENHOUSE SOILS 



The conclusions of other investigators as to the presence of protozoa 

 in the active state in normal soils led the writer to examine greenhouse 

 and field soils for the purpose of finding out, if possible, to what extent 

 the protozoa were present in the active state in the different soils. 



Twenty greenhouse soils of different composition and texture were 

 examined, each for half an hour, a new sample being placed on the 

 slide every two minutes. These samples were all taken at a depth of i 

 inch from the surface. The examinations were all made in the green- 

 house. The results are given in Table I. 



From Table I it is seen that protozoa can and do exist in the active 

 state in greenhouse soils. Their presence, however, is very limited, 

 as they were found in but 6 out of the 20 soils examined. All the soils 

 in which the protozoa were found were of open structure and their moist- 

 ure content was much above their optimum. A compact shale soil with 

 added manure and high moisture content did not show any living pro- 

 tozoa. Soils with a large proportion of organic matter and with a rela- 

 tively low percentage of moisture did not seem to encourage the presence 

 of active protozoa. From the data presented it would seem that the 

 moisture content is the primary limiting factor, while the texture and 

 content of organic matter are secondary. 



I In studies previously recorded (i), all the examinations were made under the low power of the micro- 

 scope, as it was not possible to distinguish between motile bacteria and what might be called "protozoa." 

 In the studies referred to, no difficulty was encountered in seeing protozoa which were as small as species 

 of Bodos or Monos; hence, the data collected in this study are based on the examinations made under the 

 low power of the microscope. 



