EXPERIMENTAL STUDY OF THE OYSTER GILL 



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dilution in which the test for 5. coU is positive. If, for instance, B. coli is present in 

 1 cubic centimeter but not in 0.1 cubic centimeter the value is 1; if present in 0.01 

 cubic centimeter the value is 100. The score for the whole sample is the total of these 

 values. Sometimes, however, one or more tubes show results, for instance in 0.01 

 cubic centimeter, while the other tubes show negative results in 0.1 cubic centi- 

 meter. In this case the recession of values is made; the 0.01 tube is given the value 

 10 instead of 100, while the tube showing absence of B. coli is given the value 10 

 instead of 1. The results of the test are expressed in a tabular form. 



Table 1.— Method of scoring ; ' 



The weak point in the method of scoring consists in the fact that the figures of 

 the score do not represent exact quantitative values and are used simply as symbol^ 

 to express the relative abundance or scarcity of a given microorganism. Sometimes 

 instead of a standard method a so-called "individual" method of scoring is used. 

 It consists in planting shell liquor from five separate oysters instead of making one 

 composite sample. The counting is done in the same manner as prescribed by the 

 standard method. The comparison between the two methods made by Hasseltine 

 (1926) shows that the scores obtained by the individual method may be much lower 

 than that obtained by the standard. For instance, the sample of five oysters tested 

 by the individual method scored 5 while the same examined by the standard rnethod 

 gave a score of 5,000. Such a discrepancy is undoubtedly due to the error in the 

 method of sampling. In order to get reliable results many more oysters should be 

 examined, but this involves so much labor and time as to make it impracticable^- ,^ 



The question of the standards of purity of the oysterwas much discussed during the 

 past 17 years and different standards of purity were proposed by several laboratories. 

 The bacteriological examinations of oysters were supplemented by an inspection of 

 the beds from which the oj^sters were obtained and by the bacteriological examina- 

 tion of the water. Finally, the B. coli score not exceeding 50 was accepted by all 

 parties interested in shellfish control as a permissible standard of purity. The com- 

 mittee on standard methods of the American Public Health Association (1922) failed, 

 however, to recommend a definite standard of purity, and the members of the com- 

 mittee have limited their report to a description of the methods of examination 

 without committing themselves to any definite figure. For many years various State 

 and municipal authorities regarded oysters produced imder satisfactory circumstances 

 and having a B. coli score of not over 50 as safe. In 1925 the Committee on Sanitary 

 Control of the Shellfish Industry of the United States Public Health Service recom- 

 mended that pending the collection and analysis of further data the standard of a B. 

 coli score not exceeding 50 be continued, with the understanding that if the facts 

 collected warrant it this recommendation would be altered. 



