180 
IOWA ACADEMY OF SCIENCE 
is advantageous from two wholly different reasons. They carry 
considerable quantities of plant food, particularly nitrogen. This is 
the chemical side which has been in the past perhaps unduly em- 
phasized. There is another equal and in some cases greater 
advantage derived from the application of farm manures, because 
of the large amount of nitrifying bacteria which they carry to the 
soil.” 
This opinion expressed by the scientist agrees with that expressed 
by the practical man, and they both voice the general idea in regard 
to the function of the bacteria in the manure. But here we find a 
mistake has been made. There may be numerous bacteria in the 
manure but they have nothing to do with the growth of the clover. 
When they are taken away the clover grows just as well. 
But this by no means settles the bacteriological question. A count 
of the number of bacteria was made on March 17, 1906, or 77 days 
after the loess pots were treated and planted, and 73 days after 
the till pot was planted. The media used for the first count was 
gelatine of rather poor quality and much liquefaction took place 
and the count was uncertain. A few days later another count was 
made using agar, and this proved entirely satisfactory. The results 
of both counts are given in the following table: 
Gelatine 
Media 
Agar 
Media 
Pot 
* Soil 
Treatment 
Bac. 
per. 
g- 
Molds 
per 
g- 
Bac. 
per 
g. 
Molds 
per 
g- 
44 
Loess 
Check 
100,000 
2.400.000 
7.500.000 
1.300.000 
15,000 
1,000,000 
4,000,000 
14,000,000 
700,000 
32,000 
41 
Loess 
Manure .... . . 
3,000,000 
150.000 
200.000 
240.000 
300.000 
70,000 
46 
Loess 
Man. Ster 
65 
Till 
Check 
As was expected, the second count gave larger numbers but they 
should be depended upon rather than the first figures. It is seen 
that there are a great many more bacteria in the soil that had been 
treated with the manure than in the untreated soil. This means 
that the manure made a good medium for growth of the bacteria. 
It is also true that clover grows a great deal better on the manured 
soil, and the question now is, what connection, if any, do these two 
facts have with each other. 
The sterile manure as soon as it touched the soil was inoculated. 
The untreated soil was low in bacterial life, not because it lacked 
inoculation, for all kinds of bacteria were there, but because the 
