Considerable variations were observed in the percentage of total protein soluble in 5% sodium chloride (' soluble protein ') of the minced whole muscle of North Sea cod. It was found that by assaying certain myotomes freed from myocommata, rather than whole minced fillets, much of the variation in the results disappeared, especially that caused by changes in the body lengths of the fish.Determinations spread over a period of 14 months, however, have indicated that starvation and certain phases of the reproductive cycle can bring about changes in the amount of soluble protein of such myotomes from fish of different sizes, possibly as a result of a drain on the resources of the fish.The observations made it possible to eliminate several causes of variation in the amount of soluble proteins obtained under standard conditions, and obtain material with less than I yo variation. This material will provide the basis for research on freezing and cold-storage of fish.

Measurements have been made of the percentage of total myotome protein soluble in 5% sodium chloride (‘soluble protein’) of frozen cod fillets. It was found that the soluble protein content decreased at a steady rate when the fillets were stored at − 14°, in contrast to the findings of some other workers. When the limiting value had been reached, after about 15 weeks, no further decrease was observed even in fillets stored for over 4 years at this temperature. Freezing increased the variation in soluble proteins of individual fish in a given batch considerably over that found in an unfrozen batch. The speed at which the fish were frozen was found to have no effect on the soluble protein value provided that the fish were not stored in the frozen state.

LOVE et a1.-PROTEIN DENATURATION I N FROZEN FISH. X 259 PROTEIN DENATURATION IN FROZEN FISH. X.*-Changes in cod muscle in the unfrozen state, with some further observationson the principles underlying the cell fragility method By R. M. LOVE, M. M. AREF,? M. K. ELERIAN, (the late) J. I. M. IRONSIDE, ELEANOR M. MACKAY and M. G. VARELASA study was made of the changes in the muscle proteins that occur when cod are kept in ice, using both protein extractability in salt solution and cell fragility ' values as criteria. The results by the two methods did not agree, and the reason for this is discussed with the aid of photomicrographs of homogenates of cod muscle. I t appears that changes in extractability are the consequence of a binding together of structural protein molecules and perhaps myofilaments, while a binding together of myofibrils is the agent causing changes in cell fragility readings. Cold storage changes the fragility of the cells (breakdown to fibril level), while bacterial action during stowage in ice changes the fragility of the myofi brils.

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