86 



BACTERIOLOGY OF THE OYSTER. 



The subsequent jirocedure should be the same as that recom- 

 mended by "Standard Methods" and the method of scoring should 

 be the same except that the score as obtained by this method should 

 be multiplied by two, because we are using Y2 c-c 1-20 c.c. and 1-200 

 c.c. of the original shell liquor instead of 1 c.c, 1-10 c.c. and 1-100 c.c. 

 as recommended by "Standard Methods." 



The advantages of this method are that we are basing our exami- 

 nation upon twenty-five oysters instead of five and the result will be 

 much nearer the true bacterial content of the sample. 



Another point worthy of consideration by the Committee on 

 "Standard Methods" is the number of bile tubes to be used in the 

 different dilutions. The writer in all the work reported in this paper 

 and for a long time previous has used duplicate tubes. An interesting 

 feature of this method is that both tubes from each dilution show gas 

 only approximately two-thirds of the time. The writer has regarded 

 gas in either of the two duplicate tubes as positive for the dilution and 

 has assigned it the value as recommended by "Standard Methods." 

 By using this method approximately thirty-three per cent, more B. 

 coli are found than would be the case if only one tube were used. 



"Standard Methods" under "Illustration of the Application of the 

 Method of Rating Oysters for B. coU" recommends the transferring 

 of a positive result in a high dilution in one oyster to a lower dilution 

 in another oyster, if in the latter oyster the B. coli test is negative 

 in the lower dilution. Below is an illustrated case from "Standard 

 Methods:" 



Case C. Results of B. Coli Tests in Dilutions Indicated. 



140 = rating. 



But suppose in this sample the tubes have been inoculated in dupli- 

 cate instead of one tube for each dilution. The following table shows 

 a not unexpected result : 



