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The preservation method of Perkins (1962) using suspensions in skim‐milk was used to preserve 33 bacteria and 22 fungi on anhydrous silica gel. During storage at room temperature, 64% of the bacteria and 77% of the fungi survived 1 year or more. Storage at 4° often increased the survival period c. 2‐ to 3‐fold: 73% of the bacteria and all 12 of the fungi tested at 4° survived > 1 year. At the last testing, 60% of the bacteria and 36% of the fungi were still viable after storage at 4° for periods between 3 and 4 years. The Gram positive bacilli tended to survive the silica gel preservation process better than most Gram negative bacilli. Some factors influencing survival after preservation on silica gel are discussed; the results support the use of a closed storage tube.

The freshwater mussel Anodonta cygnea and four marine shellfish (mussels, Mytilus edulis; cockles, Cerastoderma edule ; clams, Mya arenaria ; Scrobicularia plana) from a total of six sites were surveyed for Escherichia coli, Clostridium perfringens, faecal streptococci, 25 and 37 ° C coliforms, 25 ° C and 37 ° C total viable numbers and fluorescent pseudomonads . The A . cygnea from an urban lake contained greater numbers of the faecal indicator bacteria than animals from a rural lake . There were also differences in the other bacterial counts and these were discussed with respect to bacterial parameter and animal characteristics . When freshwater mussels were transferred from the city site to the rural site for 24 h the load of faecal indicator bacteria was eliminated or significantly reduced . Other bacterial types took longer to become stabilised . Loss of indicator bacteria from Anodonta was also demonstrated using cleansing in the laboratory . Very high bacterial numbers were found in some marine molluscs notably Scrobicularia plana and most shellfish contained significant numbers of the three faecal indicator bacteria at every sampling occasion . The relationship between bacterial types was discussed and it was concluded that in both freshwater and marine animals the bacterial numbers were determined more by sampling site than by species of shellfish .

The dissected digestive tract of edible mussels from two sites was examined for Escherichia coli and the counts compared with those from the total tissue of parallel mussel samples. The method using 4 x 1 ml pour plates was preferred to the 1 x 4 ml pour plate or to the 2 x 0.2 ml spread plates. Counts from the digestive tract were up to sixfold higher than parallel counts using total tissue. Digestive tract inoculum also produced amplified Esch. coli detection when lightly polluted mussels were examined by the semi‐quantitative percentage‐clean technique. It was concluded that dissection of the bacteriologically rich digestive tract significantly increases the sensitivity of Esch. coli detection and has application in environmental assay procedures using mussels or other filter‐feeding molluscs. Significant differences in the frequency of Esch. coli biotypes from the two mussel locations could be related to small differences in the pollution regimes at these two sites.

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