196 



BIOCHEMICALLY IMPORTANT MINERAL ELEMENTS 



prisingly enough, is the feeding of arsenic in the salt supply at a con- 

 centration of 25 ppm. 



Availability of organic and inorganic combinations 



Much work has been done to determine whether inorganic forms of 

 the mineral elements can supply the needs of the body for these elements. 

 With respect to phosphorus and iron the answer today seems to be clearly 

 in the affirmative. Moreover, inorganic phosphorus and iron not only 



Courtesy of A. L. Moxoii and the South Dakota Auiieultuial Kxperiincut Station. 

 Fig. 8-6. Hind feet of a cow suffering from selenium poisoning. 



can supply the requirements of the body but seem actually to be more 

 useful than some organic forms of the elements. The iron of hemin 

 and similar porphyrin compounds is unavailable to the body. In the 

 case of sulfur it is clearly established that some of the sulfur must be 

 present in the form of methionine, thiamine, and biotin. These sub- 

 stances cannot be synthesized from inorganic sulfur, and, hence, a part 

 of the sulfur supply must be furnished to the body in organic form. 

 Sulfates and other forms of sulfur, however, are utilized. The observa- 

 tion that milk is the best available source of calcium probably can be 

 attributed to the high digestibility of this food rather than to the presence 

 of a particular calcium compound. Extremely poor utilization of the 

 calcium of spinach is due, doubtless, to its reaction with the oxalic acid 

 in this foodstuff to give insoluble calcium oxalate. In general, it may be 

 said that, with the exception of sulfur as noted above, and probably 

 cobalt which is needed in the form of vitamin B12 (p. 249), the bodily 

 needs for the various mineral elements may be met entirely satisfactorily 

 by simple inorganic salts of these elements. 



