COMMEECIAL EGGS IN 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 multiplied by 9 gave the nmnber 

 of cubic centimeters of sterile physiological salt solution required to 

 make a 1 to 10 dilution, the slight error due to the gravitj^ of the egg; 

 material being disregarded. After very thorough shaking, 1 cc of 

 the 1 to 10 dilution was transferred by 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 eaclx 

 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 

 couiiting 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 NUMBER OF ORGANISMS CAPABLE OF LIQUEFYING GELATIN. 



In a number of the experiments to be reported an attempt was 

 made to determine the gelatin liquefying organism^s 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 number 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. 



