244 G. C. SuppLEer, W. A. WHITING, AND P. A. Downs 
variability was increased to 34.2 per cent from samples that were piled 
in a solid block. This variation of 34.2 per cent is the resultant of larger 
and smaller variations from compound groups of the entire block of plates. 
The coefficients of variability of 10.7 per cent and 12.3,per cent from samples 
on the tops of all piles and from all plates in the corner piles, respectively, 
when compared with the higher coefficients of variability of 19.4 per cent, 
69.7 per cent, and 61.3, per cent from those samples in positions less favor- 
ably situated, certainly indicate an important consideration in judging 
the reliability of the 37° count. 
In order to determine to what extent variations in temperature within 
the solid block of plates were responsible for discrepant counts, an attempt 
was made to obtain temperature records at different places in the pile wich 
a recording thermometer. In the absence of a more delicate apparatus, 
temperatures were determined with a Tycos recording instrument. All neces- 
sary precautions were observed in order to duplicate the normal temper- 
ature conditions from which the foregoing counts were obtained. These 
records, showing the temperature for each hour until the desired temper- 
ature of 37° was reached, are shown in table 6. Determination 1 is made. 
from the empty incubator at a point midway between the top and the 
bottom; determination 2 was made under the same conditions except 
that the bulb of the thermometer was placed inside a petri plate; deter- 
mination 3 was obtained with the bulb inside the fifth plate from the 
bottom of a single pile of 12 plates; determination 4 was the result of 
having the bulb inside the fifth plate from the bottom of a pile corres- 
ponding to pile 13 in the block of plates shown in table 4; determinations 
5 and 6 were produced from plates in the same position in piles corres- 
ponding to numbers 15 and 8, respectively, of the same table. The 
vertical distance from the top of the incubator to the plate containing 
the thermometer bulb is the same as that to one of the plates included 
in determining the average count of the fourth ample from the top. 
