Andrew Cunningham 



eo 



protozoa-free cultures had each received about 353 millions, the 

 protozoa cultures on the other hand 440 milHons of bacteria. The 

 solutions employed were similar to those used in the last experiment. 

 It was found advantageous to incubate all the cultures for two days 

 with equal inoculations of protozoa-free culture before inoculation with 

 bacteria or bacteria + protozoa as the case might be. The solutions 

 were incubated for a total period of 20 days, from the first inoculation, 

 at 22° C. The protozoa were present in observable numbers in two 

 days after inoculation — i.e. four days from the first inoculation with 

 bacteria. The ammonia was determined by distillation with magnesia 

 and the results so obtained (after deduction of controls) are shown in 

 Table 17. 



Table 17. 



Number of 



Mgs. nitrogen as ammonia in solution containing : — 



In spite of the fact that the protozoa cultures started out with an 

 inoculation of 87 millions or about I more bacteria than the protozoa- 

 free cultures, they give a markedly lower figure for ammonification. 

 The averages are, for the protozoa-free cultures 20-3 mg. N, and for 

 the protozoa cultures 15-4 mg. N. This difference lies well outside the 

 limits of experimental error. 



In the last experiment which it has been possible to carry out in this 

 direction, the bloodmeal cultures were inoculated, as above described, 

 with .580 millions bacteria and 480 millions bacteria + protozoa (as 

 indicated by counts on agar at 22° C). The conditions were otherwise 

 the same as in the previous experiment. The quantities of ammonia 

 produced in the cultures after 20 days at 22° C. are shown in Table 18. 

 (Controls have been deducted.) 



It is unfortimate that in this case the original inoculation of bacteria 

 in the bacteria 4- protozoa cultures was so much smaller than that in 

 the bacterial cultures. The experiment is, therefore, of little value in 

 helping towards a solution of the question. 



