14 BACTERIOLOGY OF THE OYSTER. 



needle in the hay stack. Moreover the incubation period of typhoid 

 varies from two to three weeks and this would make the period of 

 infection two or three weeks before suspicion would be thrown on the 

 oysters. That is, two or three weeks would elapse after infection, 

 before we began to look for the organism. During this space of time 

 the other oysters of the same laying would, in all probability, have 

 time to rid themselves of the organisms, provided they too were 

 infected. In the case of an epidemic of typhoid due to eating raw 

 oysters, the time to examine the oysters for typhoid bacilli would be 

 at the moment they were eaten. We may be quite sure from the 

 history of the cases that the oysters which were consumed did 

 contain B. typhosus, but we have no assurance that all the oysters 

 of that particular bed contained the organism. There is great 

 variation in the number of sewage organisms contained in the indi- 

 vidual oysters of the same bed. This individual variation will be still 

 greater if the bed is large and the amount of sewage small, tho highly 

 infected with B. typhosus and other sewage organisms. Sewage 

 does not ordinarily contain typhoid bacilli in constant numbers at 

 any time and unless there is an extensive epidemic, B. typhosus would 

 appear only intermittently and then in comparatively small numbers. 

 In view of these facts the wonder is, considering that B. typhosus 

 die off rapidly, both in sea water and in oysters, that typhoid bacilli 

 have ever been found at all. 



The spread of cholera through infected oysters has not attached so 

 much attention as the transmission of typhoid. The latter is distribu- 

 ted much more widely throughout the world and the opportunity 

 for such transmission is much greater. Occasionally, however, there 

 has appeared references to the spread of cholera through infected 

 oysters. In 1849 there was a small epidemic of cholera in England 

 which was attributed to eating oysters. In 1893 Sir Richard Thorne 

 attributed a number of scattered cases of cholera in England to the 

 consumption of oysters. Recently it has been reported that a large 

 extent of oyster beds in Italy have been destroyed because they were 

 thought to be a menace to the public health on account of the danger 

 of the cholera infection. 



In most, if not all epidemics of typhoid from infected oysters or 

 other articles of food, there have been a greater number of cases of 

 gastro intestinal disturbances which have not developed into 



