Feb. 14,1916 
Longevity of Soil Micro-organisms 
933 
gram of sand was determined by the plate method, samples being taken 
from two flasks representing each suspension solution. Nitrogen-free ash 
agar was used for all plates and these were kept 10 days at a temperature 
of 22 0 to 25 0 C. before counting. 
It is evident from Table I that the counts are irregular and not such as 
to form a basis for any positive conclusions. This is due in part to the 
fact that the fluctuations in numbers from time to time were so extreme 
that it was difficult to determine what dilutions should be used to obtain 
plates from which accurate counts might be made. One great mistake in 
this trial was the addition to the sand of a quantity of moisture which was 
sufficient to permit the multiplication of the organisms for three weeks 
after inoculation of the flasks. In later trials the addition of less moisture 
lessened the period of multiplication. The bacteria were not actually 
subjected to desiccation until after January 27, by which time the differ¬ 
ence in the numbers of organisms developing on the five different sub¬ 
stances was such that a fair comparison of their water-retaining capacity 
during the process of drying was not possible. Although it is true that 
after a desiccation period extending over almost four weeks (from the 
last of January to February 24) there were greater numbers of living 
organisms in the flasks to which the albumin solution had been added, 
it is possible that this would not have occurred had not the organisms in 
those flasks reached enormous numbers just previous to the period of 
drying, because of the superior nutritive qualities of this substance. 
TablF I. — Longevity of Pseudomonas radicicola , dried in sand after suspension in 
different solutions 
Date. 
Salt 
solution. 
Agar 
solution. 
Gum-arabic 
solution. 
Starch 
solution. 
Gelatin 
solution. 
Albumin 
solution. 
Jan. 2 a . 
7 . 
15 . 
27. 
Feb. 13. 
24. 
60,000 
27,400 
I, 711,000 
674, 800 
1,000 
” 5 ° 
60, OOO 
428,700 
3,651,000 
328, OOO 
1,000 
“ 5 ° 
60,000 
30,000 
63,160 
60, OOO 
— 1,000 
50 
60,000 
60,500 
2,143,000 
468,100 
— 1,000 
50 
60, 000 
626, 400 
3,974, 000 
i, 335 > 6 oo 
10 , OOO 
" 5 ° 
60, 000 
— 10, 000 
(?) 
3,677,000 
30, 000 
200 
Initial counts. 
Another experiment of the same nature was made with the following 
solutions: 
(1) Physiological salt solution. 
(2) Physiological salt solution + 0.1 per cent of agar. 
(3) Physiological salt solution + 0.1 per cent of gelatin. 
(4) Physiological salt solution -f 0.1 per cent of gum arabic. 
(5) Nutrient broth. 
(6) Milk. 
(7) Soil solution (extracted from garden soil, sandy loam, by the method of 
Van Suchtelen). 1 
1 All soil solutions were furnished by Hr. J. Frank Morgan, Research Assistant in Bacteriology. 
