NUTRITIVE VALUE OF FISH AND SHELLFISH 531 



of the analyst. The analysis of cod proteins is very low in iciuine, 

 and this perhaps may be explained in the same way. 



The data given in the table indicate that the proteins of whale 

 and beef resemble each other closely. The proteins of whale meat 

 are low in glycine, glutamic, and aspartic acids, and in proline and 

 leucine; the other amino acids exist in both whale and beef proteins 

 in practically identical proportions. 



One would hardly expect the proteins of scallop muscle to resemble 

 in composition those of chicken and beef, yet the analysis given in 

 Table 20 shows that this is the case. Except for a lower content of 

 leucine and proline and a deficiency in the nonessential amino acid 

 glycine, scallop muscle proteins are similar in composition to meat 

 proteins. 



INTERPRETATION OF ANALYSES 



Thus, it is seen that fish, scallop, and whale proteins are valuable 

 sources of nitrogenous substances for the nutrition of man and other 

 animals, for they are complete proteins, lacking only in the simple 

 amino acid glycine, which can be formed in the body by the splitting 

 of other amino acids. 



The presence of considerable amounts of tyrosine, tryptophane, 

 lysine, histidine, and arginine is noteworthy, as these amino acids 

 are essential for proper nutrition. Fishes and whale meat also 

 have been shown to contain adequate amounts of valine, leucine, 

 and phenylalanine, which are valuable constituents of proteins and 

 are also considered essential by many nutrition experts. 



Cereal proteins are, for the most part, deficient in arginine, histi- 

 dine, and lysine. The amounts of these three amino acids contained 

 in many restricted vegetarian diets are the limiting factors that 

 determine their value for maintenance and growth. The ability 

 of many Japanese to subsist on a vegetarian diet supplemented by 

 fish is due to the fat-soluble vitamins found in the fish fats and the 

 amino acids arginine, histidine, and lysine found in fish proteins. 

 The Japanese also eat considerable quantities of whale meat. Whale 

 proteins are especially high in lysine and are also high in histidine 

 and arginine, and on these accounts they are valuable in supplement- 

 ing vegetable proteins. 



Scallops also contain relatively large amounts of lysine, arginine, 

 and histidine, and for this reason furnish the amino acids deficient 

 in a vegetarian diet. Although no analyses are available to prove 

 the point, it may be assumed that the proteins of oysters, clams, 

 mussels, and other mollusks also contain adequate amounts of these 

 amino acids, which are so valuable in supplementing restricted vege- 

 tarian diets. 



SUMMARY AND CONCLUSIONS 



Fishes, mollusks, and crustaceans are rich sources of proteins. 

 Many of them are available to the wealthy and the poor alike on 

 account of their low cost. For these reasons the nutritive value 

 of the proteins of fish and shellfish is of much importance in deter- 

 mining the proper place of these foods in the diet. 



The proteins of fish, mollusks, and whale meat have been shown 

 to be easily and completely digested. The digestion products 

 consist of a nujnber of amino acids and peptids (groups of amino 



