924 NUTRITION AND HEAT REGULATION. 



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 gins, 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 

 of Voit upon isolated loops of the intestine, referred to above, show 

 that iron is eliminated from the walls of the intestine. The whole 

 history of the metabolism of iron in the body is surrounded by 

 much uncertainty. After absorption its synthesis to hemoglobin 

 takes place, as to its final stages, in the red marrow, but it is possible 

 that other organs may take part in the formation of intermediate 

 products. As regards its elimination, we know that the breaking 

 down of the hemoglobin (formation of bile pigments) occurs prob- 



