The Microbial Flora of Graded Cream. 71 



METHOD OF PROCEDURE. 



Under the direction of the state dairy commissioner, samples 

 of cream were collected from different cream stations of the 

 state and sent to the bacteriology laboratory for analysis. The 

 samples were collected in sterile bottles and kept in well-iced 

 containers until the laboratory was reached. The length of 

 time from collection to analysis ranged from twelve to forty- 

 eight hours. All samples analyzed reached the laboratory in 

 good condition. As soon as received, the flavor, odor and 

 acidity of the samples were recorded and the bacteriological 

 examination made. 



The bacteriological analysis consisted in making a quantita- 

 tive estimate of the number of organisms of the different 

 groupn present in the cream. No cultural study of the different 

 organisms was made except to demonstrate to the satisfaction 

 of the investigators that the media used for differentiating 

 the various groups were dependable. One cubic centimeter of 

 the cream was diluted in sterile water blanks until the proper 

 dilutions were obtained for inoculating plates. The following 

 media were used for differentiating the various groups of 

 organisms : 



Litmua lactose agar for differentiating the acid-producing group 



from the neutral or alkaline type of organisms. 

 Plain gelatin for determining the number of liquefiers. 

 Bile lactose agar for enumerating the colon group. 

 Laurent's yeast media for identifying the number of yeasts. 



The temperature of incubation was 37° C. for two days for 

 all media except the gelatin plates, which were held at 18° C. for 

 ten days. 



EXPERIMENTAL DATA. 



The data obtained from the few samples of cream examined 

 during the summer this grading system was established failed 

 to show, from a bacteriological standpoint, much in favor of 

 this method of grading. However, the practical results ob- 

 tained in the field seemed to warrant its use the following 

 year for further study. The complete analyses of 44 samples of 

 cream are summarized in Table 1. This gives the average of 

 the different groups of organisms present in each grade of 

 cream, and not the individual data obtained from each sample 

 of cream. Table 2 shows the percentage of the desirable and 

 undesirable types present in first- and second-grade cream. 



