APPARATUS FOR PLATING OUT PETRI DISHES IN 
THE FIELD. 
BY L. S. ROSS. 
For some time bacteriologists interested in water or 
sewage analysis have realized the fact that for determin- 
ing the number of bacteria per c.c. the water should be 
plated as soon as possible after it has been collected. If 
the samples are collected at some distance from the labora- 
tory, recourse is had to packing in ice, which is always 
cumbersome and sometimes very inconvenient. Even then 
results will not be so accurate as those obtained by plating 
immediately after collecting. Various attempts have been 
made to plate dishes in the field, I believe without very 
satisfactory results, until last summer when I first used 
the apparatus here described. 
The refrigerator pail is a double walled galvanized iron 
or copper pail of sufficient size for a rack, holding Petri 
dishes of regulation size, to stand within the inner com- 
partment. The outer compartment has an inside diameter 
of eight inches, the inner a diameter of about four and 
three-eighths inches. • A rack holding twelve Petri dishes 
is made of three upright supports, and platforms upon 
which to set the dishes. Thin, circular metal plates four 
and one-fourth inches in diameter, for the reception of the 
dishes, are fastened to the uprights, a space three-fourths 
inch or more being left between any two plates. A 
long, straight spring is soldered to one of the upright sup- 
ports for holding each dish in position by pressing firmly 
upon the cover. The end of the spring overlaps the edge 
of the dish and is bent at right angles to prevent the dish 
from slipping from its place upon the platform. A lid fits 
( 7 ) 
