572 MARINE PRODUCTS OF COMMERCE 



Sanitary precautions similar to those enforced in the United States are used 

 in European countries. Artificial purification of shellfish by chlorination is prac- 

 ticed in England. Before World War II France used a unique method of purifying 

 oysters by keeping them in sea water filtered through stone filters. Large purifica- 

 tion tanks of that type were in operation in Marseilles harbor. 



The "R" Rule 



Common belief that oysters should not be eaten in the months whose names 

 do not contain the letter "r" is not based on fact. Oysters can be eaten, and are 

 being eaten, at any time of year. Being highly perishable, their transportation and 

 storage during the warm season present difficulties and require additional care. 

 Furthermore, summer is the time when in many places oysters spawn. After the 

 discharge of their sex products they become watery, and contain but little solid 

 meat. As a rule, at this time they lack flavor and consistency, which develop wath 

 the onset of cold weather. There are, however, several localities in various states 

 where oysters of fairly good quality are available throughout the year. 



Chemical Composition and Nutritional Value 



The chemical composition of oyster meat is not constant, but varies over a wide 

 range depending on the quality of the oysters, the location from which they are 

 taken, the concentration of salts in the sea water, and the season. These facts 

 should be remembered in discussing the chemical composition of an "average" 

 oyster. Many analyses of oysters made in various parts of the world on different 

 species of oysters have been published. In most cases they were made for specific 

 purposes. However, from a few detailed analyses now available it is evident that 

 the solid fraction of meat of various species of oysters is high in nitrogen and 

 phosphorus-containing compounds. Both water-soluble and water-insoluble pro- 

 teins are present and carbohydrates, primarily in the form of glycogen, are found 

 in quantities varying from a fraction of 1 to 8 per cent of the wet weight. The 

 fatty bodies, usually reported as "ether extract," are present in relatively small 

 concentrations of about 1 to 1.6 per cent of fresh meat. The content of mineral 

 salts (ash) varies from about 0.5 to 2.76 per cent; it consists primarily of NaCl, 

 but contains also almost every chemical element present in sea water. Qualitative 

 spectrographic analysis of 22 samples of oyster ash, made by the U. S. Bureau of 

 Mines at the request of the U. S. Fish and Wildlife Service, showed that the bulk 

 of the samples contained Na, K, Ca, Mg, and P, and that the following elements 

 were present in low concentrations: Cu, Fe, Si, Al, Sr, Li, Rd, Ni, Ag, Ti, Zn, V, Pt, 

 Mn, Au, and Zr. 



Oysters have the ability to accumulate in their tissues uon, copper, zinc, man- 

 ganese, and probably other heavy metals. The role of these metals in the physi- 

 ology of the oyster is not known. Probably some of the metals are stored in the 

 tissues and are not actively involved in any physiological function. The problem 

 so far has been little studied. Observations conducted in the United States show 

 that excessive accumulation of copper produces green discoloration in O. virginica 

 (Galtsoff and Whipple, 1931) and that copper content in the tissues of the oyster 

 is the highest in the northern states (Rhode Island, Connecticut) and lowest in 

 the waters of South Carolina and Florida. The iron content follows the opposite 



