4 BULLETIN OF THE BUBEAU OF FISHERIES 



 "The question of a definite criterion of purity is of great practical importance, yet 

 the problem has never been studied experimentally; the proposed score of 50 was 

 accepted as standard, although no significance was estabhshed for either figure by 

 a comprehensive investigation. 



i ' In introducing the standard of purity of shellfish the bacteriologists have followed 

 the practice established in the sanitary control of drinking water and milk. They 

 met with difficulties, however, which at the beginning were not fully recognized and 

 which are caused by the very nature of the product. The oyster is a living organism 

 and can not be treated in the same manner as milk, water, or other food products. 

 It is capable of adjusting itself to new conditions in which it may be placed and 

 responds quicldy to changes in environment. The first difficulty encountered in 

 the application of the B. coli sco?e method to the sanitary control of the oyster con- 

 sisted in sudden and wide fluctuations in score, which sometimes occurred after the 

 oysters were taken from the water, and consequently the possibility of their further 

 pollution was excluded. It has been found that the B. coli score of the shell liquor 

 of the oyster kept in storage does not remain constant but increases and decreases 

 rather irregularly. It happened, for instance, that oysters tested in New York and 

 found to have a low score were shipped to Chicago, where they were condemned 

 because of a very high score. Recently Elliot (1926) made a study of the changes 

 in the bacterial content of market oysters and found that shucked and shell oysters 

 kept at room temperature show a sudden and maximum rise in total count of bacteria 

 from the second to the fourth day of storage. Unfortunately the author failed to 

 make temperature readings but specifies that the oysters were kept in a "cool base- 

 ment when the outside temperature was below freezing point." Sudden increase 

 in the B. coli score indicates that the microorganism was propagating in the oyster 

 liquor, but the increase in score after the oyster was taken from the water had no 

 relation to the sanitary conditions under which it was grown. 



It has been observed, also, by a number of investigators that there exists a 

 definite relation between the temperature of water and the B. coli score in the oysters. 

 Gorham (1912), Pease (1912), and Gage and Gorham (1925) have shown that in 

 winter the bacterial content of oysters taken from polluted waters is abnormally 

 low. Discussing this phenomenon, the investigators attributed it to the slowing 

 down of biological activity of the oyster as a result of a reduction of temperature and 

 came to the conclusion that with the decrease in temperature the oyster passes into 

 a state of hibernation. Round (1914), working on the bacteriology of oysters, came 

 to the conclusion that oysters close their shells for varying periods of time, dependiiig 

 on temperature. According to his opinion the opening and closing of the shell is 

 controlled by the rapidity of metabolic processes, which in turn are controlled by 

 temperature. He failed to support this statement with the experimental data, 

 however. Gumming (1916) has shown that January and February were the months 

 when the B. coli content of water taken at the mouths of rivers was highest and the 

 lowest for oysters taken from the same locality. 



The study of the effect of temperature on the B. coli score in the oyster was 

 handicapped by the lack of knowledge of the relation between the abundance of 

 B. coli in the water and in the oysters taken from the same locality. So little was 

 known regarding this important question that the Committee on Sanitary Control 



