68 



Stmlies on Soil Protozoa 



evolved determined (see Table 16, which gives the results after deduc- 

 tion of controls). 



Table 16. 



Mgs. nitrogen as ammonia in culture containing: — 



From the results of the bacterial counts (Table 15) one would 

 naturally expect that ammonification would be depressed in presence 

 of the protozoa. But the protozoa cultures have given an ammoni- 

 fication figure only slightly lower than that obtained in the protozoa-free 

 cultures. The difference is comparatively insignificant. When the 

 conditions prevailing in these experiments are kept in mind it seems 

 probable that the higher original bacterial content of the protozoa 

 cultures may account for the unexpectedly high ammonification number 

 obtained from them. It is probable that the ammonification in the 

 protozoa cultures, before development of the latter organisms, may 

 have been very rapid — so rapid that the subsequent fall in bacterial 

 numbers and consequent ammonifying power has been only just capable 

 of neutralising it. 



The only satisfactory method of deciding the matter seemed to be 

 the inoculation of equal numbers of bacteria into solutions ^^^th and 

 without protozoa. The microscopic method of counting bacteria was 

 employed for this purpose. But in the case of these bloodmeal solutions 

 the method was rather uncertain in its results, because of the difficulty 

 in distinguishing the smaller species of bacteria from fine particles of 

 bloodmeal, etc. The numbers of bacteria counted in the solutions, 

 as a result of plating on agar, showed wide dift'erences from those given 

 by the microscopic method. In the first set of experiments the solu- 

 tions were inoculated from bloodmeal cultures of protozoa -'- bacteria 

 and bacteria alone, respectively. The inoculations of bacteria were 

 arranged by the microscopic counting method so as to be approximately 

 equal. The cotuits on agar at 22'" C. indicated, however, that the 



