442 Mr. T. Goodey. Investigations on Protozoa in 



cropped up in abundance throughout, thus showing that they had suffered no 

 damage. 



The agar-plate method which I have used is as follows : — Sterile petri 

 dishes are poured with nutrient bouillon agar of about 05 to 1 per cent, in 

 strength, and, when cool, the surface of the agar is inoculated with a weighed 

 quantity of the soil the number of protozoa in which it is desired to ascertain. 

 Three plates, as a rule, are inoculated with each weight of soil and the follow- 

 ing are the weights of soil which have been used — 1, - 5, 0*2, 0*1, 0"05, 0*02, 

 0-01, 0-005, 0-002, 0-001, 0"0005, 0-0002, 0-0001 grm. The plates are allowed 

 to incubate for a few days and then the surface of each is examined under 

 the microscope for the presence of protozoa. The method entails the use of 

 a sensitive balance and is limited by the difficulty of manipulating such small 

 quantities of soil as are produced in weighing in the region of 0*0001 grm. 

 However, the results which I have obtained with it are fairly consistent and 

 are more trustworthy than those of the hay-infusion method, I think. 



It was my hope at the beginning of the experiment to obtain evidence, by 

 means of the counts of protozoa, concerning their activity and multiplication 

 if such were proceeding. 



Counts of protozoa were therefore made at the beginning and towards the 

 ends of the experiments. The hay-infusion method was used in the first 

 counts and the agar-plate method for the later ones. As I have pointed out, 

 the latter method gives higher counts and more trustworthy results, and one 

 cannot, therefore, strictly compare the evidence afforded by the two methods. 



For this reason I have not found it possible to obtain sound evidence as to 

 whether the protozoa have multiplied since being added to the soil. See 

 footnote, however, on p. 454. 



The Bacterial Counts. 



The results of the periodical determination of the numbers of bacteria by 

 the gelatine-plate method are tabulated below and the curves obtained by 

 plotting these results are shown in figs. 1, 2, 3, 4, and 5. 



In order to simplify matters I have arranged certain curves together, for 

 the whole nine curves when plotted all together present a confusing array 

 and do not lend themselves to easy elucidation. 



Fig. 1 shows the curves obtained from the untreated, bacteria, and 

 V. microstoma inoculated soils. 



The most noteworthy feature is the extraordinarily high bacterial count in 

 the Bacteria soil at 32 days and the subsequent drop in the numbers of 

 bacteria to a level below that of the untreated soil. This low bacterial 



