934 NUTRITION AND HEAT REGULATION. 



unchanged or unused in the feces or urine. A small portion, how- 

 ever, must be absorbed and used and a corresponding amount must 

 be eliminated as a true waste product of tissue metabolism. Voit, 

 by experiments upon isolated loops of the intestine, has shown 

 that some calcium is constantly eliminated from the inner surface 

 of the intestine. The amount is small, not exceeding perhaps 0.15 

 to 0.16 grams per day. There is some evidence that the amount 

 of calcium in the tissues increases with age. This is certainly 

 true of the bones, which become exceedingly brittle in advanced 

 life, and is evident also in the arteries, whose elasticity diminishes 

 as the calcium salts deposited in their coats are increased. Under 

 pathological conditions deposition of calcium salts (calcium car- 

 bonate) in the tissues may be markedly increased, as is shown 

 by the condition of the arteries in arterial sclerosis and the con- 

 dition of the crystalline lens in senile cataract. 



The iron salts that are constantly necessary for the production 

 of new hemoglobin are provided in our food, in which they exist 

 in organic combination. The value of the food in this respect 

 varies greatly, as may be seen from the following table selected 

 from Bunge's analysis: 



100 grns. of dry substance contain iron in milligrams, as follows : 



White of egg trace Apples 13 



Rice 1 to 2 Cabbage (green leaves) ... 17 



Wheat flour (bolted) . . 1.6 Beef 17 



Cows' milk 2.3 Asparagus 20 



Potatoes 6.4 Yolk of egg 10 to 24 



Peas 6.2 to 6.6 Spinach 33 to 39 



Carrots 8.6 



In conditions of malnutrition, particularly in the simple anemias, 

 it becomes necessary to select a diet with reference to its contents 

 in iron or to add iron deliberately to the diet. Therapeutically 

 iron may be given in the form of simple salts with organic or mineral 

 acids or in more complex organic combination. There has been 

 much controversy as to whether the body is capable of taking 

 the iron in inorganic form and synthesizing it into a molecule so 

 complex as that of hemoglobin. Experience, however, seem to 

 show that this is possible, although under normal conditions at 

 least our iron is used in organic form. Bunge first isolated such a 

 compound, a nucleo-albumin containing iron, which he prepared 

 from the egg yolk and called hematogen. This compound must 

 serve as the source of the hemoglobin in the developing chick. 

 When the diet is directed especially toward increasing the iron 

 food it would seem to be wiser to choose these compounds, or, better 

 still, the iron-rich foods, rather than medicinal preparations of 

 the inorganic salts. The daily excretion of iron from the body 

 takes place in the feces rather than in the urine. The experiments 



