BALANCE OF NUTRITION. 



871 



have been dealt with in previous articles. So far as the bodystuffs are con- 

 cerned (and to a somewhat less extent with regard to the foodstuffs), it cannot 

 be said that we possess an acquaintance so intimate as to enable us fully to 

 understand the changes which they undergo ; and as a consequence it will be 

 found that our knowledge of metabolism, in spite of the enormous amount of 

 work that has been done to elucidate it within the last five and twenty years, 

 is still in an unsatisfactory condition. 



Balance of nutrition. The first determinations that require to be 

 made in any inquiry into the metabolism of the body are those of its 

 incomings and outgoings. 1 The incomings of the body consist of food 

 and oxygen ; the outgoings, of the various excreta, and of the carbon 

 dioxide and water lost by the lungs and skin. If the incomings of the 

 body exactly balance the outgoings, so that the animal neither gains nor 

 loses weight, the body is said to be in complete nutritive equilibrium. 



Sufficient information can be usually obtained regarding the balance 

 of metabolism of the body, if the nitrogen and carbon only are determined 

 in the ingesta and egesta. 



As an instance of complete equilibrium in a man weighing 70 kilos., 

 embracing both the nitrogen and carbon of the ingesta and egesta, the 

 following balance table may be given (Burdon Sanderson 2 ) : 



We may also have a condition in which the body either gains or 

 loses weight, and in which consequently the incomings and outgoings do 

 not exactly balance one another, but during which, nevertheless, the 

 nitrogen which is taken into the body, and that which leaves the body, 

 may strike an exact balance, while the other elements which compose 

 the food and excreta, and especially the carbon, hydrogen, and oxygen, 

 may not be similarly balanced. When the nitrogen of the food exactly 

 balances the nitrogen excreted, the body is said to be in nitrogenous 

 equilibrium. Under these circumstances we may assume that the living 

 material of the tissues (which is essentially composed of nitrogenous 

 substance) is neither diminished nor increased in amount ; whereas, if 

 at the same time the other constant elements of the food the carbon, 

 hydrogen, and oxygen are met with in diminished or increased quantity 

 in the excreta, we may assume that substances in the body other than 

 the living tissues are either becoming laid on, or becoming diminished 



1 For the methods of determining these may be consulted, C. Voitin Hermann's "Hand- 

 buch," 1881, Bd. vi. S. 6 et seq., and numerous papers which have appeared since then 

 chiefly in the Arch. f. d. ges. PhysioL, Bonn (by Pfluger, Zuntz, and their pupils), and in 

 the Ztschr. f. Biol., Munchen (by Voit and his pupils). See also v. Noorden, "Grundriss 

 einer Methodik der Stoffwechsel-Untersuchungen," Berlin, 1892. For the methods of deter- 

 mining the respiratory products, see article "Chemistry of Respiration"). 



2 " Syllabus of Lectures on Physiology," 1879. 



