502 
Journal of Agricultural Research 
Vol. XXXI, No. 6 
It was obvious from the start that the high numbers recorded 
could not be correct. The volume of 1 gm. of soil is ordinarily a 
little less than 1 c. c. This space would be completely filled by 
approximately 1,000,000,000,000 (1 billion) bacteria (6 p. 17). The 
10 or more billions 4 per gram counted by Whittles undoubtedly 
originated from outside contaminations (11). But there still re¬ 
mained the possibility that after eliminating this source of error the 
use of the vibrator might insure a more perfect distribution of the 
soil organisms than is obtainable by shaking the soil dilutions by 
hand. 
THE VIBRATOR APPARATUS 
Whittles’ vibrator apparatus consists mainly of four parts: A 
vibrator cup, an electric vibrator, a reservoir for sterile diluent, and 
a sterile receiving flask. The writers constructed a similar apparatus 
in the following manner. 
The vibrator cup was made from a large-mouthed glass jar 2J£ 
inches in diameter, having an aluminum screw cap. The bottom 
of the jar was cut off, and the center of the cap removed, leaving 
only enough of it to make a good seal when screwed on. A disk or 
pyralin was fitted into this cap and a soft rubber gasket placed on 
each side to prevent leaking. When the jar is inverted the disk of 
pyralin becomes the bottom of the vibrator cup and the vibrating 
membrane. For the outlet, a hole was drilled in the side of the cup 
at the 10.0 c. c. level and a right-angle' tube with a rubber gasket 
inserted. 
The vibrator was simply an ordinary electric door bell with the 
bell removed. A rubber stopper was placed under the hammer so 
that by raising or lowering it, adjusting the screw of the make-and- 
break and the height of the vibrator cup above the hammer, the 
correct vibration of high frequency could be produced, violently 
agitating the surface of the liquid in the cup. 
The reservoir was a 2-liter Erlenmeyer flask having a siphon long 
enough to reach nearly to the bottom of the vibrator cup. The 
writers found it most convenient to sterilize the filled reservoir for 1 
hour in the autoclave at 20 pounds pressure. In order to be able to 
do this, the lower end of the siphon had to be flexible, so that it 
could be turned upward on itself, closed with a sealed rubber tubing, 
and wrapped in cotton. When ready for use, a screw clamp on the 
flexible portion controlled the flow through the siphon. The receiv¬ 
ing flask was a sterile 2-liter flask graduated at 1,900 c. c. 
STERILIZATION OF THE VIBRATOR 
The sterilization of the vibrator cup, with its pyralin membrane 
and rubber gaskets, could not be carried out in the autoclave or 
hot-air oven, nor could salts of the heavy metals be used. Alcohol 
seemed to fulfill the requirements and was tried in the first experi¬ 
ments. The vibrator cup was taken apart, soaked for 20 minutes 
in 50 per cent ethyl alcohol, rinsed with sterile water, and assembled 
under aseptic conditions. It was then placed in position over the 
vibrator, fastened with a clamp, filled with sterile water, and the 
vibrator started. As a check on the sterility of the cup, four 1 c. c. 
* See footnote on p. 1. 
