Bivalves in Relation to Disease 169 



isms from the human body may sometimes be found in 

 the water that runs away from them to our rivers and 

 harbors and bays, in very many of which, along the 

 coast, are oyster and clam beds. It is altogether prob- 

 able that other intestinal diseases may also be dissem- 

 inated by shell-fish taken from polluted waters, but not 

 so much is known of this as of typhoid fever. 



It is explained in the chapter on the feeding habits of 

 shell-fish that large quantities of water are constantly 

 being drawn within the shell and into the interior of the 

 basket-like gills. Even the minutest of solid particles 

 borne by this stream are stopped on the outer surfaces of 

 these organs and caused to adhere in masses by the pres- 

 ence of a sticky mucus. The organisms of diseases, 

 though very minute, are not small enough to escape. 

 Several gallons of water every day pass through the gills 

 of every full grown oyster or clam, and every solid- 

 particle is removed from it and remains in the body. 



This collected material is then passed on to the mouth, 

 and once in the digestive tract of the bivalve, the organ- 

 isms dangerous to man probably are eventually killed by 

 the digestive fluids. But because the collecting process 

 never ceases, at least when the creatures are continually 

 submerged as are oysters and little necks, they may be 

 present on the gill surfaces at all times. The shell sur- 

 faces also afford lodging places for them, and to handle 

 them is not safe. The organisms probably are not at all 

 injured by the gill secretions, and, carried into the human 

 digestive tract when a raw oyster or little neck is eaten, 

 will multiply and cause the disease. It is thus plain that 

 even if relatively few in the water, the chances are that a 

 dangerous number of- disease organisms will be strained 

 out of it by these shell-fish. 



