SOURCES OF CONTAMINATION. 



29 



viduals susceptible to ptomain poisoning. In fact any highly per- 

 ishable food product of this character may quickly spoil and be 

 injurious to health if not properly refrigerated under good sanitary 

 conditions. As just stated, oysters may be kept for a period of six 

 weeks under proper conditions, yet, even though they were taken 

 from unpolluted beds and stored under good sanitary conditions, 

 mere length of time alone may cause them to become unfit for use. 

 No oyster should be used when the shells show the least gaping, nor 

 when the liquor is practically all gone. 



DISEASED AND GREEN OYSTERS. 



In their study of the " Oyster and disease," Herdman and Boyce 28 

 elaborately treat the subject of green oysters. They show that cer- 



YIG. 10. Oyster floats between the row ol oyster 1 >oats (fig. 9) and the shore. Anchored from piles. Both 

 oysters and water from this locality were found to be contaminated. Sixty carloads of oysters, mostly 

 eaten raw, are shipped from this place daily in winter. Beds on which they grow arc probably uncon- 



taminated. 



tain of the green oysters are healthy, while others are not so consid- 

 ered. Some forms of greenness are described as a "leucocytosis," 

 which may be associated with an excessive amount of copper. Other 

 species may have no copper present^ but a special pigment, u ma- 

 rennin," is found with a certain amount of iron. In the present in- 

 vestigations the green oyster was frequently encountered and 

 a mounts of copper varying from 150 to 714 mg per kilogram a were 

 found, while from oysters not showing the green coloration amounts 

 varying from 14 to 40 mg per kilogram were obtained. Apprecia- 

 ble quantities of copper were also found in the water and mud b taken 



a Analysis made by W. C. Taber, Food' Inspection laboratory. 



b Analysis made by W. W. Skinner, Water Laboratory, Miscellaneous Division. 



