NUTRITION OF OYSTERS: GI,YCOGEN FORMATION AND STORAGE. 



l6l 



when the experiment was ended, to be in a nutritive condition comparable to the oysters 

 from the same source examined before the experiment. The result of chemical analysis 

 is shown in Table lo. 



Table io. — The Nutrition of Oysters by Seaweed and Protozoa.^ 



Treatment of oysters. 



Ash in 

 dried 

 meats. 



Glycogen 

 in dried 

 meats. 



Glycogen 



in ash- 

 free solids. 



Analyzed as soon as brought from beds. (See experiment i. Table 2). 



Fed with Utva lactuca during 14 days 



Fed with Protozoa cultures during 17 days 



Per cent. 



36-45 

 32.56 

 36.70 



Per cent. 



7-03 

 4-55 



Per cent. 



4-37 



10.43 



7.18 



Q The oysters used in these experiments were from the same lot. 



An attempt was made to follow the nutritive condition of the experimental oyster 

 by determinations of nitrogen in the dried tissues. From the results of 20 analyses no 

 definite conclusions could be drawn. In the various artificial feedings, changes in the 

 nitrogen content of the tissues were observed, but they were always small and in most 

 cases merely percentage changes attributable to the altered proportions of salts and 

 glycogen, rather than to a change in the actual amount of protein present. 



. SUMMARY. 



A summary of the results of this work follows: 



1 . Evidence was obtained of a seasonal variation in the glycogen content of oysters. 

 A depletion occurs in the warm weather but is followed by a storing-up process in the 

 latter part of the summer and in the fall. Glycogen seems to decrease during the cold- 

 est weather. This favors the idea of hibernation. The results on seasonal variation 

 agree with the results of Milroy. 



2. Glycogen may be formed in the oysters from dextrose. Fat storage may occur 

 simultaneously. 



3. The optimum conditions for this process are: (a) Duration of dextrose feeding 

 two to three days; (6) concentration of dextrose equal to about 0.25 per cent; and (c) 

 water density not greatly different from that in which the oysters have previously 

 been. 



4. Excess of sodium phosphate in the medium may check glycogen formation from 

 sugar. 



5. Formation of glycogen from dextrin was not obtained. 



6. Failure of glycogen formation from sugar by oysters taken from the shells was 

 observed. 



7. Evidence that Protozoa and fragments of seaweed {Ulva lact-uca) may ser\'e as 

 food for oysters is given. 



8. Decaying seaweeds lodged above oysters that are under otherwise good grow- 

 ing conditions may cause their death. 



