NUTRITIVE VALUE OF FISH AND SHELLFISH 



545 



Copper is a normal and necessary constituent of shellfish as oxygen- 

 carrying pigment of the blood, like iron in the vertebrates. It is 

 also taken up in quantity by oysters growing in the presence of 

 copper. That zinc and manganese are also probably normal and 

 physiological in some way in the lower marine animals and not 

 derived from accidental contamination is shoA\-n by data obtained 

 from 22 species of marine invertebrates around Tortugas, Fla., which 

 is in pure ocean water far removed from land. The metals occur in 

 these animals in greater concentration than they do in sea water. 

 These data are given in Table 25 (taken from Phillips, 1917). 



Table 25. — Copper, zinc, iron, and manganese in 22 species of marine inverte- 

 brates around Torlugas 



[Quantities in grams per 20-gram sample] 



In another work on Pacific coast moUusks (Albrecht, 1923) further 

 data are given on the inorganic constituents of the livers of shellfish. 

 These are shown in Table 26. 



Table 26.- 



Inorganic constituents of the livers of Pacific coast nmlliisks, 

 100-gram samples 



housed on 



In Table 26 the high percentage of mmerals in the livers, as repre- 

 sented by total ash, is significant, especially the u"on, which amounts 

 to nearly one-third of the total ash. The liver seems to serve as an 

 iron-storage body in these animals. 



Traces of arsenic have been found in oysters (Hiltner and Wicli- 

 mann, 1919). In 15 samples the minimum was 0, the maximum 1.47, 

 and the average 0.99 milligrams per kilogram or parts per billion. 

 Arsenic is found normally in human hair and nails. 



IMPORTANCE OF MINERAL SUBSTANCES IN THE DIET 



The chemical elements that occur regularly in the human body are 

 oxygen, hydrogen, nitrogen, carbon, phosphorus, sulphur, chlorine, 

 fluorine, iodine, iron, calcium, magnesium, sodium, and potassium. 

 Besides these, arsenic, copper, zinc, and manganese occur in small 

 quantities and are of unknown significance. All of these elements 

 occur in sea water and sea foods. As they are absolutely necessary 

 for normal human fife (with the possible ejcception of the last four), it 

 would be idle to discuss their relative importance. Such fundamental 

 processes of life as respiration, digestion, muscle c^jntraction, nerve 



