834 NUTRITION AND HEAT REGULATION. 



is necessary to maintain the sodium chlorid content of the blood. 

 It is employed as a condiment for its pleasant flavor, and it is 

 possible that its use is often carried to excess. This is a matter of 

 practical dietetics concerning which at present we have no satisfac- 

 tory experimental data to base a judgment upon. 



The calcium salts of the body play a most important role in 

 connection with the irritability of muscle and nerve (p. 520). 

 They are also of obvious importance in furnishing material for 

 the growth of the skeleton. Their importance in this regard has 

 been demonstrated by feeding experiments. Young dogs when 

 given a diet poor in calcium salts fall into a condition resembling 

 rickets in children, owing to a deficient growth of the bones. Pig- 

 eons also, when fed upon a similar diet, exhibit an atrophy and 

 fragility of the bones due doubtless to the lack of calcium salts. 

 As in the case of the other food materials, there must be a definite 

 calcium metabolism in the body. It is probable, indeed certain, 

 that most of the calcium salts ingested simply pass through the 

 body without entering into its structure. They are eliminated 

 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. 



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 



