CHAPTER XII 

 METABOLISM 



WHILE we have thus far considered the individual sub- 

 stances taken up and cast out by our body and have 

 explained their importance, we shall now treat of the 

 balance, or the comparative composition of the quantities of 

 the substances taken up and cast out by the body collec- 

 tively. This balance not only gives us the extent of meta- 

 bolism, but also shows us the relation and the use of each 

 foodstuff to the animal economy. At the same time we can 

 thereby learn how a person can best support himself with 

 the most appropriate food at the least expense and how to 

 bring his body to a desired state of nutrition. Upon the 

 results of this balance of metabolism is based the practical 

 science of dietetics. 



1. METHODS OF INVESTIGATION IX METABOLISM 



To strike a balance of nutrition, we must know the quan- 

 tity taken up and given off. 



The substances taken up are food and the inhaled oxygen. 



The substances cast out of the body are found in the 

 urine, faeces, sweat, expired air; smaller amounts in the 

 sebum of the skin, in the cast-off horny epithelium, hairs, 

 nails, at times in the menstrual blood, milk, and semen.' 

 Of these, as a rule, only those present in the urine, faeces, 

 and expired air are taken into account in the balance of 

 nutrition. The others are present in such small quantities 



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