Feb. 14, 1916 
Longevity of Soil Micro-organisms 
937 
plating and from one new flask each time, the object being to secure 
more representative counts. Plates were made with ordinary agar and 
kept for one week at a temperature of 22 0 to 25 0 C. before counting. 
Moisture determinations were made in duplicate at the time of each 
quantitative plating, the bacterial counts being then computed on the 
oven-dry basis. 1 Small variations in the percentage of moisture, occur¬ 
ring after the soils attained the air-dry condition (which with sand and 
sandy loam was by March 3 and with the other three soils between 
March 3 and March 29), are probably the result of fluctuations in the 
humidity of the room air. In the case of clay it was impossible to 
secure a thoroughly mixed sample, owing to its drying into a sort of 
hard, baked condition; therefore, a slight irregularity in the moisture 
determinations could not be avoided. The data are recorded in Table V. 
TabtF V .—Number of bacteria per gram in 50 grams of sand, sandy loam, clay, clay 
loam, ana muck when dried after the addition of soil solution 
10 c. c. of soil solution added. 
15 c. 
c. of soil solution added. 
Sand. 
Sandy loam. 
Clay. 
Clay loam. 
Muck. 
Date. 
Number 
Per- 
Number 
Per- 
Number 
Per- 
Number 
Per 
Number 
Per- 
of bac- 
cent- 
of bac- 
cent- 
of bac- 
cent- 
of bac- 
cent- 
of bac- 
cent- 
teria per 
age of 
teria per 
age of 
teria per 
age of 
teria per 
age of 
teria per 
age of 
gram. 
water. 
gram. 
water. 
gram. 
water. 
gram. 
water. 
gram. 
water. 
1914: 
462,900 
Nov.17 
285,200 
20.0 
170,000 
20.0 
30.0 
225,000 
30.0 
453 , 9 oo 
30.0 
Dec. 29 
1915: 
4,318,000 
14* 54 
26,170,000 
14-38 
11,500,000 
28.96 
60,840,000 
31.81 
33,689,000 
26. X3 
Jan. 28 
1,912,000 
6.25 
5,806,000 
2.81 
1,492,000 
19-17 
26,006,000 
12,798,000 
16.96 
16,6x3,000 
24-85 
Mar. 3 
197,000 
. z 
1,555,000 
1,967,000 
.84 
914,000 
3-59 
9-83 
5,782,000 
19-51 
29 
51,900 
•36 
.78 
552,000 
•93 
4,659,000 
2-93 
4,924,000 
16.33 
Apr. 21 
18,900 
. 16 
i, 066,000 
.84 
447,100 
1-57 
4,135,000 
3-31 
4,217,000 
x6.32 
May 7 
32,5°° 
.27 
983,000 
x.08 
278,800 
1.81 
3,845,000 
3-65 
2,220,000 
16.25 
14 
37,000 
.22 
2,245,000 
1.10 
378,000 
1.74 
3,914,000 
3-63 
2,703,000 
1,836,000 
IS* 9 i 
June 18 
41,000 
. 20 
3,218,000 
1.22 
494,000 
1.98 
5,456,000 
4. 26 
16.80 
Sept 6« 
127,600 
•14 
6,523,000 
1.23 
1,241,000 
2. 26 
11,686,000 
4-30 
2,781,000 
16. 78 
& This count was made by Mr. O. M. Gruzit, Graduate Assistant in Bacteriology. 
With a view to determining the predominant types of organisms 
placed in the soils, isolations were made from a few of the most common 
types of colonies occurring on the plates of the original soil solution. 
The characteristics of these organisms were studied. It must not be 
assumed, however, from the fact that so few organisms were isolated, 
that the flora of the soil solution was limited to the species observed. 
The high dilutions necessary for obtaining accurate quantitative plates 
failed, of course, to show up the organisms which were present in smaller 
numbers. From the quantitative plates made after the soils reached the 
air-dry state, between March 3 and May 7, isolations were made of the 
most numerous types. As the muck plates were frequently overgrown 
with a downy white mold, but few pure cultures could be obtained from 
1 Dried at 105 ° C. for 94 hours. 
