200 THE ECONOMIC IMPORTANCE OF ANIMALS 



$15,000,000 a year has been derived during the last decade from such 

 sources. Hundreds of boats and thousands of men are engaged in dredg- 

 ing for oysters. Three of the most important of our oyster grounds are 

 Long Island Sound, Narragansett Ba^, and Chesapeake Bay. 



Sometimes oysters are artificially " fattened " by .placing them on beds 

 near the mouths of fresh- water streams. Too often these streams are the 



bearere of much sewage* 

 and the oyster, which lives 

 on microscopic organisms, 

 takes in a number of bac- 

 teria with other food. 

 Thus a person might be- 

 come infected with the 

 typhoid bacillus by eating 

 raw oysters. State and 

 city supervision of the 

 oyster industry makes this 

 possibility very much less 

 than it was a few years 

 ago, as careful bacterio- 

 logical' analysis of the 

 surrounding water is con- 

 stantly made by com- 

 petent experts. 



Clams. Other bivalve 

 mollusks used for food are 

 clams and scallops. Two 

 species of the former are 

 known to New Yorkers, 

 one as the " round," an- 



This diagram shows how cases of intestinal disease 

 (typhoid and diarrhea) have been traced to 

 oysters from a locality where they were " fat- 

 tened " in water contaminated with sewage. 

 (Loaned by American Museum of Natural 

 History.) 



other as the " long " or 

 "soft-shelled "clams. The 

 former ( Venus mercenaries) 

 was called by the Indians 

 "quahog," and is still so 

 called in the Eastern states. The blue area of its shell was used by the 

 Indians to make wampum, or money. The quahog is now extensively 

 used as food. The " long " clam (My a arenaria) is considered better 

 eating by the inhabitants of Massachusetts and Rhode Island. This 

 clam was highly prized as food by the Indians. The clam industries of 



