THE RELATION OF DIET TO DISEASE 437 
experiments showed that breast-fed aiiimals contained 
about six times as much iron as the milk that nourished 
them. The iron content of all these animals is highest 
at birth, remains constant during the suckling period and 
then rapidly decreases to the adult standard. After this 
level is reached the iron metabolized must be supplied 
from the food if the hemoglobin is to be spared. 
The functions of all these inorganic substances are 
intimately interrelated and in places interchangeable. 
Calcium is capable of correcting disturbances of inor- 
ganic equilibrium in the animal body whatever the direc- 
tion of the deviation from the normal may be. These 
interrelationships are most involved in the maintenance 
of body neutrality. The normal processes of metabolism 
involve a continual production of carbonic, phosphoric 
and sulphuric acid which must be immediately disposed 
of if the neutrality of the body is to be permanent. 
The factors involved in this are carbonates, phos- 
phates, ammonia and proteins. Carbon dioxide is the 
chief excretory product but is at the same time a normal 
constituent of the blood and as such, is an important 
factor in this physicochemical regulation. There is a 
tendency for the respiratory mechanism to hold its carbon 
dioxide tension nearly constant. Late investigations have 
shown that lowering of this tension is an early sign of 
beginning acidosis. When food such as protein, is taken 
in excess the strongly acid residues are neutralized by 
the sodium and potassium carbonates which are elimi- 
nated with a corresponding loss of sodium and potassium. 
The carbon dioxide tension diminishes, 37.2 per cent, on a 
high protein as against 43.3 per cent, on a vegetable diet. 
If this excess is long continued, the result may be, and 
often is, an increased elimination of the base-forming ele- 
ments which if not made good tends to diminish the body's 
reserve alkalinity. A diet with a preponderance of basic 
elements leads to an alkaline urine with an increased uric 
acid solvencv and an increased carbon dioxide tension 
