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 of the quantities of the substances taken up and cast 

 out by the body collectively. This balance not only gives 

 us the extent of metabolism, 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 IN 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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