Purification of Polluted Oysters

Abstract

The danger from typhoid fever and other enteric diseases to which consumers of raw oysters, contaminated by intestinal or urinary discharges, are subject, has been too well established by a number of careful epidemiological studies to permit any doubt concerning its possible magnitude. With regard to the disposal of sewage in America and Europe, they have definite sanitary rules and regulations for the purpose of keeping oysters free from contamination by human excrement. According to the results of one of the author's bacteriological analysis of oysters¹⁾ collected from the principal oyster producing areas in Japan, about 90% of our oysters are suitable to be sold without further comment and nearly 10% of them belong to the group for further analysis and condemnation. In other word. 10% of our oysters must be cleansed by any methods of purification. Since the bacterial contents of oysters are closely correlated with the bacterial contents of the sea water in which they are grown, it is possible for oysters to cleanse themselves when transplanted from polluted water to water which is clean. So that, the best way to cleanse the polluted oysters is the trans-plantation to the clean sea water, free from contamination with sewage. As a matter of fact, there are so many cases that we can not find any natural clean sea water suitable for the purification of polluted oysters by floating within a reasonable distance. In these cases it is necessary to search for any artificial purification. This need for a method of artificial purifica-tion, which exist also in other localities, lead to the development of many processes such as D_ODGSON¹⁰⁾, C_HABAL¹²⁾, F_ABRE-D_OMERGUE⁹⁾, W_ELLS¹¹⁾, T_ARBETT¹⁶⁾, F_ISHER¹⁵⁾, C_ALMERIA¹⁴⁾, I_NWOOD¹⁸⁾, B_{LUE POINT} C_O.¹⁷⁾ and others. We picked up some of them which are acknowledged as more important and tried the experiments following to their principles as possible as we can, installating of wooden tanks of 550-560 litres and the bacteriological procedures adopted to the American Standard (A. P. H. A.)¹⁹⁾.
The results of artificial purification are, generally speaking, good with these methods of T_ARBETT, D_ODGSON and C_HABAL and could be applied in practical application with little modification in Japanese oysters and clams, especially the T_ARBETT'S method gave the superior results. On the contrary, for the methods of F_ISHER and I_NWOOD would be necessary some improvement and exeercise in their managements. The experiments with cockles and trough-shells, we expect to study more in order to put into practical application. One of the results of D_ODGSON'S method and the summarized results of artificial purification done by us are shown in the tables 1 and 2. Next, we can conclude that the length of time necessary for the purification from polluted oysters to unpolluted oysters will suffice within 24 to 48 hours, if the waters exactly clean and about 7 days will enough when the water to which the oysters are transplanted is occasionally subject to slight pollution as experienced in the waters of Kanazawa Bay, Kanagawa Prefecture, Japan.