THE R6tiE OF PROTEIDS IN METABOLISM 409 



animal is given a diet with a constantly increasing amount of proteid food 

 from day to day, after a few days the total nitrogen found in the excreta 

 exactly balances that taken in the food. This condition of nitrogenous 

 equilibrium is established at different levels, varying sometimes according to 

 the individual and with the kind and quantity of other food principles taken 

 at the same time as the nitrogenous foods. 



Chittenden's latest metabolism experiments have shown that with free 

 choice, but moderate use, of accessory articles of diet, the human body can 

 maintain itself in nitrogenous equilibrium for at least several months on an 

 average of 4 to 10 grams of nitrogen per day, the equivalent of 25 to 62.5 

 grams of proteid. 



The Role of Proteids in Metabolism. The proteids of food are 

 described by Voit as having two relations to the proteid metabolism and to 

 outgoing urea; the first part going to maintain the ordinary and quiet metab- 

 olism of the tissues, for which purpose it is actually built up into the living 

 protoplasmic molecule, and the second part causing a more rapid formation 

 of urea, but never becoming a part of the actual protoplasmic molecule. The 

 former proteids are called mor photic or tissue proteids, the latter circulating 

 or floating proteids. Normally more proteid is eaten than is needed to sup- 

 ply proteid to the protoplasm for growth, as has just been stated. Pfliiger 

 takes the view, however, that the tissues must have an excess of proteid to 

 destroy in order to perform their metabolic processes normally. This use 

 of the proteids to form heat by their oxidation, and not to produce tissue, was 

 looked upon by the older physiologists as a wasteful use of good material, 

 and was called a luxus consumption. 



Folin has recently announced a theory of proteid metabolism in which 

 he calls special attention to the relation of the nitrogenous excretion products 

 to the nitrogenous intake. He has shown that the urea contained in the 

 urine varies almost directly with the quantity of proteid in the food; that 

 the ammonia varies with the proteid in the food; that the uric acid decreases 

 (and increases) with the proteid in the food, but not in direct ratio; while the 

 creatinin excreted is " wholly independent of quantitative changes in the total 

 amount of nitrogen eliminated." 



TABLE SHOWING THE OUTPUT or NITROGEN IN A NORMAL, HEALTHY INDIVIDUAL 



ON A FOOD RICH IN NITROGEN, JULY i3TH, AND POOR IN NITROGEN 



JULY 20TH (FOLIN). 



July i ath. July aoth. 



Volume of urine 1,170 c.c. 3850.0. 



Total nitrogen 16.08 grams 3. 60 grams 



Urea-nitrogen 14-7 ' = 87.5 per cent 22.0 " = 61.7 per cent 



Ammonia-nitrogen.... 0.49 =3.0 0.42 =11.3 



Uric-acid-nitrogen 0.18 ' 



Kreatinin-nitrogen 0.58 ' 



Undetermined nitrogen 0.85 ' 



= 1.1 " 0.09 " = 2.5 



= 3.6 " 0.60 



= 4.9 " 0.27 



