174 THE WEALTH OF THE SEA 



The value of a given substance as food depends 

 not only upon the nature of its digestion products 

 but also on the ease with which it is digested. 

 Leather contains much protein, yet its nutritive 

 value is negligible because it is indigestible. Before 

 we can evaluate the fats and proteins of fish we 

 must consider their digestibility. Contrary to what 

 many persons believe, scientists have found that both 

 the fat and protein of fresh and canned fish are as 

 easily and completely digested as the fats and pro- 

 teins of meat. 



Dr. Holmes, of the U. S. Department of Agri- 

 culture, studied the digestibility of the fat and pro- 

 tein of mackerel, grayfish, butter-fish, and salmon, 

 and reported that they were easily and completely 

 digested. Dr. Holmes concluded: "the very com- 

 plete utilization of the proteins and fat supplied by 

 the fishes studied offers additional experimental 

 evidence that fish is a very valuable food and that its 

 extensive use in the dietary is especially desirable." 



Nutritive Value of Fish 



Since the chief food constituent of fish is protein, 

 it is interesting to examine these proteins to see 

 whether or not upon digestion they furnish all of 

 the amino-acids needed for the building up of the 

 complex protoplasmic structure we call our body. 

 Perhaps, before going further, it would be well to 

 indicate the nature of amino-acids, the wonderful 

 compounds of which our muscles and many of our 

 other tissues are constructed. These acids are inert, 

 colorless solids which contain nitrogen, being very 



