76 SHELLFISH 



district, and ranks as one of the purest localities in England for 

 the growth and fattening of oysters. Houston says it is a river 

 which "on topographical grounds, has been, and would still be 

 considered eminently well suited for the breeding, growth and 

 fattening of oysters for market." 



The following results were obtained by Houston with oysters 

 from this source, while the sea water results are also included for 

 comparative purposes. 



Helford sea water. 



B. coli or coli-like microbes in B. enteritidis sporogenes 



100 C.C. 10 C.C. I C.C. 10 C.C. 



Positive result Positive result Positive result Negative result 



28% 40% 3'% ioo /o 



Helford oysters. 



B. coli test. 



i out of 25 (4/ ) contained i B. coli or coli-like microbes per oyster. 

 5 >t (20%) 10 



16 ,, (64%) > I0 " 



3 > ( I2 /o) > 1000 



B. enteritidis sporogenes test. 



1 6 out of 25 (64 / ) contained less than 10 spores per oyster. 

 8 j, 25 (32 / ) contained 10 but less than 100 spores per oyster, 

 i 25 (4%) 100 1000 



(c) Oysters from estuaries seriously contaminated with sewage. 

 The Penryn River is polluted and its oyster layings lie under the 

 ban of suspicion. " The Penryn River, on topographical and 

 epidemiological grounds, would be regarded with great suspicion, 

 if not condemned." 



The following results were obtained by Houston. 



_. .'."...<" ' -i 



Penryn water. 



B. coli or coli-like microbes in B. enteritidis spcrogenes 



10 c.c. i c.c. o'r c.c. o-oi c.c. to c.c. 10 c.c. 



Positive Positive Positive Positive Positive Negative 



result result result result result result 



-16% 36/o 44/o 4 Q /o' 56 C / 44% 



