NUTRITION OF OYSTERS: THE NATURE OF THE SO-CALLED 

 "FATTENING" OF OYSTERS. 



By PHILIP H. MITCHELL. 



Ccmtributiaii from the United States Fisheries Biological Station, Woods Hole, Mass., and the Biological 



Laboratory of Brown University. 



INTRODUCTION. 



The term "fat" as applied to oysters refers in a popular sense to their appearance. 

 When in that condition the meats look plump and have in the body portions a milky 

 appearance not unlike emulsified fat. The juice running out of the meats, however, 

 shows the opalescence characteristic of glycogen solutions. This, together with the 

 fact that glycogen is shown by analysis to be especially abundant in some specimens of 

 oysters and to vary greatly in different specimens, suggest the possibility that glycogen 

 may be the chief if not the only substance increased in oysters when they become 

 "fat." 



In a previous paper" it was shown that glycogen shows seasonal variations in 

 oysters and that an increase of glycogen accompanies favorable feeding conditions. 

 It was also shown that glycogen storage not only accompanied the normal feeding 

 process, but could occur as the result of assimilation of sugar in solution in the water 

 utilized by oysters. 



This paper presents evidence in the form of chemical analyses'" of oysters in varying 

 nutritive conditions to show that the amount of glycogen present is the only material 

 which marks a notable difference between "fat" and "lean" oysters. 



VARIATIONS OF PROTEIN IN THE OYSTER COMPARED WITH THOSE OF GLYCOGEN. 



The percentage of glycogen or protein in whole oyster meats is not a useful index 

 as to their nutritive condition or their value as human food. The great variations in the 

 proportion of water present in oysters are obvious causes of apparent variations in 

 other constituents when figured as percentages. It goes almost without saying that 

 the results of analyses must be expressed in terms of percentage of dry substance. An 

 equally important variable is the salt content. Ash determinations made under com- 

 parable conditions have shown in these analyses variations from 1 4 to 37 per cent of the 

 dried weight. It is therefore necessary in comparing determinations of glycogen, 



o " Nutrition of oysters; Glycogen formation and storage," Bull. Bureau of Fislieries, vol. xxxv, 1915-16, pp. 151-161. 

 b Part of the analytical work presented in this paper was done by A. E. Barnard. 



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