Andrew Cunningham 63 



To sunimarise the results of these experiments on the effects of 

 temperature and moisture on the soil protozoa : — It has been shoum 

 that some, at least, of the jj-rotozoa in soils lead an active life and are capable 

 of multiplyinff to quite a considerable extent when (he conditions become 

 favourable. It is also very probable thai those protozoa which do lead an 

 active life in soils {as indicated by the dilution method) are capable of 

 liinitiny the numbers of bacteria present in the latter. But this point 

 still re([uires some elucidation. 



W . The Influence of Protozoa on the numbers of 

 Bacteria nEVELOPiN(; in A:\imonifvin(; Solutions. 



In order to obtain some information on the capacity of soil protozoa 

 for destroying bacteria in solutions, it was thought necessary to have 

 a method of suppressing the former. In the literature one finds that 

 P. T. Mtiller^ employed Saponin for this purpose, in connection with 

 his investigations on the protozoa of swimming-baths. The concen- 

 tration used was -5 % and it is stated that this had no injurious action 

 on the bacteria. 



The use of Saponin was, therefore, applied to ammonifying solutions 

 inoculated with soil. I % bloodmeal in water was heated to one and 

 a half atmospheres in the autoclave and filtered. -05 % KoHPO^ was 

 added and 100 c.c. of the solution sterilised. After cooling this nutrient 

 solution was inoculated with 5 grams, of garden soil and incubated for 

 18 hours at 22° C. The bacterial content of the .solution was determined 

 (agar, incubated at 22' C, has been used as medium for bacterial counts 

 all through this section and the results are stated in the tables as millions 

 per c.c). The solution was divided into two equal parts in small sterile 

 flasks and one portion received -5 % saponin. Plates were poured from 

 both portions at the intervals indicated in Table 12. 



The active protozoa present were counted by the microscopic 

 method. The immediate eft'ect of the saponin is seen in the depression 

 in the numbers of bacteria in the solution. This, however, does not 

 last long. After 24 hours the protozoa developing in the solution without 

 saponin begin to exercise a decided depressing effect on the number 

 of bacteria and this has continued throughout the experiment. But 

 the contrast between the bacterial contents of the two portions is 

 doubtless somewhat minimised because the saponin has failed to 

 suppress entirely the protozoa. 



' -tcr/)./. Hijij. Bd. 75, 11112, p. 3l'1. 



