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84
Although the Report by title refers to shellfish other than oysters, these latter to
some extent are dealt with.
The Report deals with the places from which mussels and cockles are found, and
maps are given illustrating the text.
"Mussels and cockles are found very largely at or near the mouths of estuaries,
"a fact which renders them liable to be affected by the pollutions which are not
"uncommonly brought down by the waters of such estuaries."
Dr. Bulstrode points out that:—
"Fortunately, the history of past outbreaks of enteric fever and gastro-enteritis
"which have been associated with the consumption of shellfish has shown that the
"shellfish in question have been collected from localities and beds which were
"obviously liable to pollution ; and, although having regard to the history of water"borne
epidemics of enteric fever and cholera, it cannot be affirmed that distant
"sources of pollution may not at times be operative for harm, it is quite clear that
"were all the proximate sources of pollution removed, there would be a verv material
"decrease in the number of cases of enteric fever which are now attributable to
"shellfish."
And after dealing with difficulties and limitations of bacteriological analysis he states
that in the meantime a useful provisional standard is one based on topographical and
epidemiological grounds.
"No pretence is made that a standard thus based is satisfactory or final, but it
"is one which, if intelligently acted upon, should lead to very great improvement
"in the conditions under which shellfish are now gathered, and which may not
"improbably save from greater disaster an important industry."
The instructive part of the Report deals with the control and purification of sewage,
which, as he points out, has not been adequately appreciated by those who have had to
deal with the pollution of shellfish, pollution either in its scientific, practical, or legal
aspects.
"Unfortunately, however, the difficulties connected with sewage purification
"have not yet been exhausted, and the important additional statement has to be
"made that at present there is no practical method of sewage treatment apart from
"sterilisation which will afford guarantee against the presence of organisms of
"intestinal origin in the effluent. With the discovery of ' septic tank ' treatment
"it was hoped that a method for the destruction of pathogenic organisms had been
"secured, but recent work has shown that neither the septic tank alone nor in
"combination with 'bacterial' filter beds will suffice to remove the sewage
"organisms; and in dealing with the sewage problem this is one of the difficulties
"which have to be faced."
Attention is called to the practice, in constructing a sewerage system, of constructing
the sewers of such a size and gradient as will enable the dry weather flow to pass to
the outlet at a certain velocity, and this renders it necessary to construct storm overflows,
which come into operation when the dry weather flow has perhaps been diluted five
or six times or more.