176 THE WEALTH OF THE SEA 



calcium and phosphorus, for the bones are usually 

 eaten as well as the flesh. Fish bones consist largely 

 of calcium phosphate, which is needed by the human 

 body for the growth and repair of bones and teeth. 

 It is therefore fortunate that many persons prefer 

 canned salmon and tuna to fresh fish, probably be- 

 cause they are well cooked, and the bones do not 

 cause any bother. Pressure cookers should be used 

 for cooking bony fish. When a fish containing many 

 fine bones, as the shad, is cooked with steam under a 

 few pounds pressure, the bones become almost as soft 

 as the flesh, and are then quite edible. This eliminates 

 the tedious and disagreeable operation of picking out 

 the bones, and thus not only adds to the pleasure 

 of eating fish, but also increases their nutritive 

 value. 



The old idea that fish is a "brain food" probably 

 has little foundation, but perhaps fish roe may have 

 that distinction. For the roe contains certain or- 

 ganic phosphorus compounds also found in the hu- 

 man brain, which are called phospholipins because 

 they resemble fats chemically. It is likely that the 

 human body utilizes these unusual compounds for 

 building up the gray matter in which so many per- 

 sons are deficient. 



Recently a lack of iodine in food and drinking* 

 water has been recognized ,as one of the principal 

 causes of endemic goiter, cretinism, and other dis- 

 eases of the thyroid gland. The active principle of 

 the thyroid gland, thyroxin, is an iodine compound. 

 If our food does not contain sufficient iodine to 



