64 BACTERIOLOGY OF THE OYSTER. 



found in varying numbers. Herdmann and Boyce sum up the 

 matter as follows: "The result was definite and uniform; there was 

 a great diminution or total disappearance of B. typhosus in from one 

 to seven days." 



Johnstone^ took oysters known to be polluted and transferred 

 to the purest water available. He found under the conditions of 

 the experiment that four days was a sufficient period of quarantine, 

 since after that time no further cleansing took place, because the 

 water of the locality was not entirely free from sewage contamination. 



Phelps in this country^ found that only two to four days was 

 necessary for polluted oysters to cleanse themselves when transferred 

 to clean water. 



In 1913, Fabre-Domergue^ read a paper before the Academic de 

 Medicine in which he recommended the placing of polluted oysters in 

 basins fed by filtered water and removed often enough to insure com- 

 plete evacuation of the Hquid contained in the shells and in the 

 digestive tract. From his results he considers it an established fact 

 that this procedure eliminates all pathogenic bacteria from the mol- 

 luscs in six or seven days. 



Field* says: "These (oysters) get bacteria from the waters filled 

 with waste and sewage, and it takes them at least seventy-two 

 hours to free themselves from these impurities that they have taken 

 in from the waters of the different harbors." Field does not say upon 

 what evidence, if any, this statement is based. But he adds that 

 in Massachusetts a law has been passed requiring such polluted 

 oysters to be transferred to clean water and allowed to remain for 

 four weeks before offered for sale. 



The writer's own experiments on the cleansing of polluted oysters 

 confirm in part the work cited above. It appears that the rapidity 

 with which sewage bacteria are eliminated is influenced to quite a 

 large extent by the temperature. If the water is warm, say around 

 20° — 25 C. the oysters remain open probably most of the time. 

 As this is about the optimum temperature for the most rapid growth 

 and development of the oyster, it is also the temperature at which 

 the oyster is most active. The ciliary motion is more rapid than at 

 lower temperatures which would increase the amount of water 



iJour. of Hyg IX, 1909. 



*Jo'.ir. Am. Public Health Assn., Vol. 1, 1911, 30-5. 



^Cited in Jour. Am. Med. Asso., LXI, 1913, 134. 



Report of Proceedings of 3rd Am. Convention of Nat. Asso. of Shellfish Commission, p. 34. 



