THE OYSTER. 43 



out the microscopic organisms that float in the water. 

 Many gallons probably many barrels of water are 

 drawn through the gills of each oyster every day, and 

 the microscopic beings "that it may contain strained out 

 and entangled upon the surface of these natural strain- 

 ers, and pushed along towards and into the oyster's 

 mouth, in a stream that, while almost as slow as the 

 movement of the minute hand of a watch, is steady and 

 almost uninterrupted. Each microscopic organism is a 

 long time in travelling from the point where it first 

 touches the gill into the oyster's stomach. All this 

 time it is alive, and capable of reproducing its kind and 

 becoming the parent of new generations, when removed 

 from the gill and placed under suitable conditions. 

 Most of these organisms are wholesome to man, and all 

 that enter into the oyster's stomach are quickly killed 

 and converted into its palatable and nutritious sub- 

 stance, but, so long as they are travelling along the 

 gills, all are alive, and some extremely dangerous to 

 man. The oyster exercises choice in the selection of 

 its food, rejecting some of the microscopic organisms, 

 and swallowing others ; but those that are discharged 

 into the water with the sewage of cities are not, unfor- 

 tunately, among the ones that are rejected; and before 

 these have entered the oyster's stomach, they are most 

 favorably placed for gaining entrance into human 

 stomachs and multiplying there. 



It has been known to naturalists for many years that 

 epidemics of cholera and typhoid fever have arisen 

 through the contamination of oysters by sewage ; and, 



