MINERAL METABOLISM 383 



Since an egg contains approximately 1.1 nig. of iron, laying hens some- 

 times do not receive enough of the element. 



Milk contains little iron and the level is not raised by feeding iron 

 to the mother. Therefore, most deficiencies in otherwise normal in- 

 dividuals occur in nursing young. The fetus accumulates iron, but 

 prolonged nursing without other foods richer in iron than milk may 

 allow exhaustion of the supply. 



Physicians have claimed that lack of iron produces the commonest, 

 clinically manifest deficiency disease of man. The dietary form is en- 

 countered in infants while that due to chronic blood loss occurs 

 primarily in women. Anemia is invariably observed and is charac- 

 terized by reduced numbers of red cells which are abnormally small 

 and which are pale in color due to the reduction in iron. Simple iron- 

 deficiency anemias respond quickly to the administration of ferrous 

 sulfate. In more complex situations, copper or cobalt may also be 

 necessary. Deficiencies due to lack of B12 or folic acid produce anemias 

 but of the macrocytic or giant-cell type. In addition to this symptom 

 of iron deficiency, others that may appear include any combination of 

 listlessness, chronic fatigue, palpitation of the heart, lesions of the 

 mouth and tongue, abnormalities of the finger and toe nails, and 

 changes in the composition and appearance of the bone marrow. 



The growth of pigs immediately after birth is unusually rapid, and 

 when kept in concrete pens out of contact with the soil they cannot 

 forage for the iron they need. Consequently piglets develop deficien- 

 cies rapidly when reared in modern quarters unless they are given 

 iron. Feeding iron to the sow does not help since the element does 

 not appear in the milk. The simplest effective treatment is provision 

 of a trough of soil or sod for the pigs to eat. Anemia, lack of ap- 

 petite, poor growth, and labored breathing are characteristic and often 

 accompanied by a flabby appearance and edema of the head and fore- 

 body. 



Iron anemia is not observed in poultry except perhaps during heavy 

 egg laying and then of only mild type and probably not detrimental to 

 the birds. Grazing animals develop anemias in certain areas in 

 Florida where both soil and herbage are rather low in iron. However, 

 it is now suspected that the trouble may actually be a deficiency of 

 either copper or cobalt. Other than this possible case, herbivores seem 

 not to develop iron deficiencies under field conditions. 



Magnesium 



This element occurs in animals in motlerate amounts with about 

 75 per cent of the total in the teeth and skeleton. In these tissues 



