BACTERIOLOGICAL PROCEDURE. 11 



decidedly higher than 10 cc per oyster, the average recorded hy 

 Houston. In some cases this average was as high as 15 cc per oyster, 

 including both liquor and body meat. The quantity of course 

 varied according to the size and shape of the oyster shell. 



Some preliminary work was done in order to decide upon the best 

 and most practical method to follow. Individual oysters from the 

 same lot were treated in various ways. Oysters obtained from 

 clean, hard bottoms showed little difference in results when com- 

 pared with those from the same source thoroughly scrubbed. Oysters 

 from muddy bottoms showed the greatest necessity of cleaning 

 before being opened. Practically the same method with slight modi- 

 fications was used during the entire work. Only sound, representa- 

 tive stock was considered. 



The examination of composite samples of five or more oysters was 

 supplemented by inoculating media with the liquor from single oys- 

 ters to determine the presence of Bacillus coli in each. It was also 

 decided to use only the liquor bathing the oyster, instead of both 

 meat and liquor, as the latter represents the character of the whole 

 contents of the shell sufficiently well to determine the presence of 

 pollution. 



MEDIA EMPLOYED. 



Plain agar and nutrient beef broth. Prepared according to the standard methods 

 )mmended by the American Public Health Association. 56 



Bile salt agar. Prepared after the formula of MacConkey 41 by adding 0.5 per cent 

 sodium taurocholate, 2 per cent peptone, 1 per cent lactose, and 1.5 per cent powdered 

 agar to a liter of water. To this mixture a sufficient quantity of a 1 per cent solution of 

 neutral red is added to give a light red color to the finished medium. The bile salt 

 agar is used as a differential medium for the isolation of B.-coli-\ike colonies. Plates 

 are incubated from twenty-four to forty-eight hours, when the colon bacilli, if present, 

 will appear as smooth, round, raised, entire, glistening, pink colonies. 



Litmus milk fermentation tubes. Used for the determination of the presence of B. 

 enteritidis sporogenes. 



In addition to the media already mentioned, the following were 

 also tried, but because of unsatisfactory results their use was not 

 continued : Gelatin, lactose agar, litmus lactose agar, Endo's medium, 

 Hiss's agar, and plain agar without the addition of salt. 



PLATING SAMPLES. 

 WATER. 



Solid cultures. In the routine water work the following cultures 

 are made for each sample: 



(a) Plate 1 cc, 0.1 cc, 0.01 cc, and 0.001 cc on plain agar at 25 C. 



(6) Same dilutions on plain agar at 37 C. 



(f) Same dilutions on bile salt agar incubated at 37 C. 



Plates are incubated from two to four days, according to temper- 

 ature. 



