_Shell-fish_ have recently claimed the attention of bacteriologists, owing to the outbreak of typhoid and other epidemics apparently traceable to _oysters_.
It is four or five years since Professor Conn startled the medical world by tracing an epidemic of typhoid fever to the consumption of some uncooked oysters.[71] Almost at the same time Sir William Broadbent published in the _British Medical Journal_ a series of cases occurring in his practice which illustrated the same channel of infection. Since then a number of similar items of evidence to the same effect have cropped up. Hence there is little wonder that a number of investigators concentrated their attention upon this matter. Professors Herdman and Boyce, of Liverpool, Dr. Cartwright Wood, Dr. Klein, and Dr. Timbrell Bulstrode are some of the chief contributors to the elucidation of this problem.
The mode of infection of oysters by pathogenic bacteria is briefly as follows: The sewage of certain coast towns is passed untreated out to sea. At or near the outfall, oyster-beds are laid down for the purpose of fattening oysters. Thus they become contaminated with saprophytic and pathogenic germs contained in the sewage. It will be at once apparent that several preliminary questions require attention before any deductions can be drawn as to whether or not oysters convey virulent disease to consumers. To the solution of these Dr. Cartwright Wood was one of the first to address himself.
The precise conditions which render one locality more favourable than another in respect to oyster culture are not fully known. But it has been observed that they do not flourish in water containing less than three per cent. of salt. Hence they are absent from the Baltic Sea, which, owing to the fresh water flowing into it in rivers, contains a smaller percentage of salt than three. Oysters appear in addition, to favour a locality where they find their chosen food of small animalculæ and particles of organic matter. Such a favourable locality is the mouth of a river, where tides and currents also assist in bringing food to the oyster. Unfortunately, however, in a crowded country like England such localities round her coasts are frequently contaminated by sewage from outfalls. Thus the oysters and the sewage come into intimate relation with each other.