were put in glass containers and placed in an oven 

 at 50° C. for about 1 hour. The meats were then 

 removed witli a glass spatula from the gaping 

 valves. The shell liquor remaining in the con- 

 tainers was added to the meats, and a sample of 

 10 oysters was weighed and placed in a porcelain 

 dish for drying at 90° C. to a constant weight. 



The dried samples were pulverized in a glass 

 mortar. Then several grams of the powdered and 

 well-mixed sample were weighed into a silica dish, 

 charred over a low flame, and ashed in an electric 

 muffle at a temperature of 500° C. for 3 to 4 hom-s. 

 After cooling the sample was moistened with water 

 and 1 ml. of concentrated nitric acid was added. 

 The sample was evaporated to dryness on a hot 

 plate and returned to the muffle, this time at a 

 temperature of 400° C. One application of nitric 

 acid was usually sufficient to complete ashing. 

 Ash was dissolved by heating in a 1:1 solution of 

 hydrochloric acid, 10 drops of hydrogen peroxide 

 were added, and heat was applied imtil the libera- 

 tion of oxygen ceased. Finally the sample was 

 weighed, transferred to a 100-ml. volumetric flask 

 and diluted to the 100 ml. mark. 



For iron determination Kennedy's colorimetric 

 method of potassium thiocyanate was emploj'ed 

 (Kennedy, 1927), using ferrous ammonium sulfate 

 (dried to constant weight) as standard. Copper 

 was determined by Biazzo's method as described 

 by Elvehjem and Lindow (1929) and Elvehjem 

 and Hart (1931). Zinc was determined by 

 Birclviier's method, using a nephelometer for 

 comparison of the turbidity of samples (Bh-ckner, 

 1919) and zinc oxide solution in hydrocliloric acid 

 as the standard. Manganese was found by 

 Richards' method (Richards, 1930). To determine 

 the reliability of analytical procedures, several 

 analyses were made in duplicate and occasionally 

 known cjuantities of metal salts were added to the 

 samples and recovered. In this way error due to 

 analytical procediues was found to vary between 

 0.5 and 2.5 percent. 



Differences in the results of analyses of oyster 

 meat often are due to the method of obtaining 

 samples. Tlie percentage of solids in a sample and 

 the corresponding figure of moisture content de- 

 pend on the method of drying. Sometimes the 

 sample is dried on a steam bath at a temperature 

 of 90° C; in otlier cases the oyster meat is kept in 

 an electric oven at 95° or 97° C. The results will 

 also differ if the sample is first homogenized or if 

 the whole oyster is used for tlrying. 



The main source of inconsistency in the analyses 

 results from methods of discarding the fluid 

 retained in the mantle cavity and in the water 

 tubes and chambers of the gills. This fluid con- 

 sists primarily of sea water with some blood cells 

 and excretion from the kidney. Oysters removed 

 from the shell with no injury to the mantle and 

 pericardium nevertheless continue to lose blood 

 from the severed ends of the muscle and from 

 blood sinuses in the body proper. The loss of 

 body fluid is very rapid during the first half horn* 

 after removal from the shell. For as long as 2 

 hours after shucking the oyster may lose a quantity 

 of fluids equivalent to 26 percent of the original 

 body weight (Fingerman and Fairbanks, 1956a, 

 1956b). Puncturing the mantle and pericardium 

 results in up to 50-percent loss of body weight. 



To minimize losses of weight caused by pro- 

 longed bleeding, oyster meats may be placed on a 

 screen and drained for 5 minutes. More consistent 

 results are obtained if the water captured between 

 the organs is discarded. If the valves are forced 

 apart slightly and jammed open by a small 

 wooden wedge, sliaking the oyster with 10 sharp 

 jerks is sufficient to dislodge the water from the 

 gills. This method gives a lower percent of solid 

 content than those obtained with other procedures, 

 because bleeding is minimized. 



The percent of moisture in the meat is usually 

 determined by the difference between the total 

 and dry weight of the sample. Direct determina- 

 tion of water content can be made by distillation 

 in xylene in a flask with a reflux condenser. The 

 sample is boiled continuously for 1 hour at a rate 

 of approximately 5 ml. of reflux per minute and 

 for 3 hours at double that rate. Without interrupt- 

 ing the boiling, two drops of 95 percent ethanol 

 are added through the top of the condenser. After 

 the violent ebullations have ceased, boiling is 

 continued for 5 minutes (Calderwood and Piechow- 

 ski, 1937), then the volume of water accumulated 

 in the side arm of the condenser is measured. 



The glycogen content of oyster tissues is deter- 

 mined by digesting them in 30 percent sodium 

 hydro .xide for 1 hour at 80° C. Glycogen is 

 precipitated by 95 percent ethanol, washed, dis- 

 solved in hot water, hydrolyzed with hydrochloric 

 acid for at least 4 hours at 92° C. and the dextrose 

 present determined in aliquot sample by use of the 

 Hagedorn-Jensen procedure. Details modifying 

 the method to make it suitable for obtaining 

 glycogen in a high state of piuity from oyster 



CHEMICAL COMPOSITION 



385 



