Sept. 15. 191S Soil Protozoa 541 



to the increased toxicity produced from the decomposition products of 

 bacteria and other organisms. It is very clearly noted that in all inocu- 

 lated solutions as soon as the maximum development is reached there 

 is a gradual decrease in numbers of all types of organisms. In so far as 

 observations have been made, this fact is attributed to several causes: 

 The soil contains various kinds and numbers of Uving organisms as well 

 as spores and many cysts. If the temperature and other conditions, such 

 as sufficient desirable food, the absence of harmful toxins, and the presence 

 of favorable reactions (acidity or alkalinity) are present when a culture 

 solution is inoculated with the soil, certain types of protozoa as well as 

 other organisms excyst and multiply until conditions become unfavorable. 

 Owing to the lack of desirable food for certain species of organisms, the 

 presence of certain decomposition products of either bacteria, yeasts, 

 molds, or protozoa, or the direct destruction by other forms, the organ- 

 isms either encyst or die. The organisms probably remain inactive until 

 conditions again become favorable, when they excyst and multiply as 

 before. 



TYPES OF PROTOZOA DEVELOPED IN DIFFERENT CULTURE SOLUTIONS 



In hay-infusion solutions inoculated with the greenhouse soil the 

 organisms observed corresponded to Vorticella spp., Colpoda cuctdlus, 

 Colpidium colpoda, Prorodon ovum Ehrb., and Glaiwoma sp. The first 

 two mentioned appeared the second day after inoculation; the others 

 were first noted on the sixth day. In some solutions a few of these 

 forms were still present on the thirtieth day. No vorticellae devel- 

 oped from any inoculations with field soil, indicating that this form 

 inhabits rich moist soil. This fact has already been noted by several 

 investigators. In hay infusion several different unidentified types devel- 

 oped. This has never before been obser\^ed in any of the other culture 

 solutions. A large type of flagellates developed on the third day after 

 inoculation. In some solutions of hay infusion these forms appeared 

 soon after the smaller ones had disappeared. Colpoda was the most com- 

 mon form of ciliate in inoculations with field soil. From inoculations of 

 field soil types of ciliates developed different from those in solutions to 

 which greenhouse soil was added. It was also noted that fewer types 

 of organisms were developed from the former than from the latter soil. 



In hay infusion the large ciliates were markedly different from those 

 which had already been observed with dried-blood extract. In the 

 former solution inoculated with greenhouse soil but one type was 

 observed. It was very apparent that dried-blood extract was the most 

 favorable for the development of many types of large ciliates. 



On the ninth day after the inoculation in hay infusion to which field 

 soil had been added millions of very minute organisms that appeared 

 to be flagellates were noted. These could barely be recognized under 

 the low power of the microscope. This form was not counted, but was 



