COMMERCIAL EGGS 11^ THE CENTRAL WEST. 75 
METHOD OF PLATING AND COUNTING. 
The flask containing the portion for examination was weighed. 
The weight of egg material in grams multij)lied by 9 gave the number 
of cubic centimeters of sterile physiological salt solution required to 
make a 1 to 10 dilution, the slight error due to the gravity of the egg 
material being disregarded. After very thorough shaking, 1 cc of 
the 1 to 10 dilution was transferred hj means of a sterile pipette to 
9 cc of sterile physiological salt solution, thereby obtaining a 1 to 
100 dilution. Higher dilutions were made on the same plan. Two 
duplicate series of plates of nutrient agar were prepared from four 
consecutive dilutions. One set was incubated at 37° C. for two days ; 
the other for five days at 20° C. 
The history of the sample was used as a basis for deciding in eacli 
case which dilutions should be plated. Whenever possible plates 
containing from 50 to 250 colonies were selected for counting. The 
numerical results were expressed in accordance with the rules pre- 
scribed by American Public Health Association, 1912. A Stewart's 
counting chamber and a hand lens, magnifying four or five diameters,. 
were used to facilitate the counting. To determine the sterility of the 
media, the salt solution, and glassware, blank plates were poured at 
each plating. Plates of agar were also exposed to the air for three 
minutes during each plating to show the relative freedom from air 
contamination. 
DETERMINATION OF THE NUMBEJR OF ORGANISMS CAPABLE OF LIQUEFYING GELATIN. 
In a number of the experiments to be reported an attempt was: 
made to determine the gelatin liquefying organisms quantitatively. 
For this purpose gelatin plates were prepared at the same time and 
in the same manner as the agar plates. These were incubated at 
20° C. and the liquefying colonies counted at the most appropriate 
time. The counts were so discordant that many of the results were 
discarded. The difficulty appeared to be due principally to the 
fact that in most cases there was present a mixture of organisms, 
some of which were capable of liquefying the entire plate in 48 
hours while others required several days, or even weeks, to show the 
first signs of liquefaction. The action of the slower ones was, there- 
fore, masked by that of the more rapid. 
After a large num]5er of gelatin plates had been made and it was 
found that irregular counts were very frequent, it was decided to 
abandon the method except in special instances where special in- 
formation was required. 
DETERMINATION OF THE NUMBER OF ORGANISMS PRODUCING GAS FROM LACTOSE 
IN THE PRESENCE OF BILE SALT. 
At the time of plating 1 cc of each dilution was transferred to a 
Durham fermentation tube containing lactose bile salt medium. 
