Feb. 14,1916 
Longevity of Soil Micro-organisms 
935 
Table III .—Longevity of Pseudomonas radicicola , dried in sand after suspension in 
different solutions 
Date. 
Salt solu¬ 
tion. 
Agar solu¬ 
tion. 
Gelatin 
solution. 
Gum- 
arabic 
solution. 
Albumin 
solution. 
Broth. 
Milk. 
Soil solu¬ 
tion. 
April 16. 
May 3. 
1,648,000 
“25 
2,144,000 
25 
1,901,000 
-as 
116 
3,234,000 
-25 
360,000 
56 
2 
i,477»ooo 
428,625 
432,000 
4,026,000 
515 
106 
1,266,000 
39i 
3»o8o 
The figures in Table III offer little except a general confirmation of 
the results of the two other experiments. As the sand was air dry after 
April 26, it may be understood that the counts on May 3 and May 13 
represent the numbers surviving 7 and 17 days desiccation, respectively. 
Attention must be called to the fact that the lack of figures to show the 
comparison in increase of bacteria in the different solutions between 
April 16 and April 26 makes it impossible to overlook entirely the func¬ 
tion of these different solutions in their nutritive capacity. Plates were 
made on April 26, but the nitrogen-free agar made up with maltose 
instead of saccharose proved an unfortunate choice; for no colonies 
whatever developed, although, as seen by the two subsequent platings, 
living organisms were then present in abundance. However, the favor¬ 
able influence of the soil solution, whether it may be as a food material 
for soil organisms or a protection during desiccation, can not be disputed. 
An experiment was conducted to compare the longevity of P. radi¬ 
cicola dried in quartz sand and in clay-loam garden soil. As in the fore¬ 
going experiments, the organism was grown for five days at room tem¬ 
perature on nitrogen-free ash agar. The bacterial growth from one agar 
slant was transferred to 12 c. c. of physiological salt solution and the 
mixture shaken thoroughly, and 1 c. c. of the suspension was diluted 
and plated quantitatively. To the two flasks each of clay loam and 
quartz sand were added 2 c. c. of the bacterial suspension. The clay 
loam had been sifted and air dried. The quartz sand had been prepared 
after Rahn’s method, described previously. Fifty-gm. portions of each 
were placed in 100 c. c. Erlenmeyer flasks plugged with cotton and steril¬ 
ized by heating in the autoclave for 45 minutes under 15 pounds' pressure. 
The inoculated flasks were shaken to distribute the organisms through¬ 
out the sand or soil, and then kept in a dark, well-ventilated place at a 
temperature of 22 0 to 25 0 C. The number of living organisms per gram 
of sand and loam was determined at intervals by plating quantitatively 
from two samples of each. 
Table IV .—Difference in longevity of Pseudomonas radicicola dried in quartz sand and 
in clay-loam soil 
Date. 
Sand. 
Clay loam. 
Atvril t6 . 
I, 648, OOO 
25 
I, 648, OOO 
42,133 
33 .o 2 5 
Mav ^. 
0 . 
T2... 
*0 . 
