226 THE URINE. 



seuts a minor but more constant source. The actual amount that is 

 eliminated is thus primarily dependent upon the amount ingested. 



The total urinary nitrogen is under normal conditions practically 

 equivalent to the quantity ingested, barring the small fraction which 

 escapes digestion in the feces. Such a condition is spoken of as the 

 nitrogenous equilibrium of the body. Of this, however, different 

 levels may exist, which may vary in the same individual, If the 

 amount of nitrogenous food is thus diminished, the amount of 

 urinary nitrogen will also decrease ; and if the amount of food then 

 remains constant, the nitrogenous output will likewise remain the 

 same. If, on the other hand, more nitrogen is now ingested, an 

 increased elimination will result ; but a certain fraction is retained 

 by the body, and gradually a higher level of equilibrium becomes 

 established. 



There are natural limits to this power of accommodation, how- 

 ever, and we finally reach a point which varies in different indi- 

 viduals, where a further increase in the amount of nitrogen that is 

 ingested does not lead to a higher level of equilibrium, and where 

 consequently a further retention of nitrogen does not occur. Over- 

 feeding then results in various digestive disturbances diarrhoea and 

 vomiting occur, and the body thus protects itself against an undue 

 accumulation of circulating albumin which it would not be able to 

 dispose of in a normal manner. 



Underfeeding, on the other hand, gradually leads to an increased 

 destruction of the organized albumins. For a while the reserve of 

 fats and carbohydrates is still capable of protecting the body against 

 an unduly rapid loss of nitrogen from this source, but death finally 

 results. 



From the fact that the level of nitrogenous equilibrium is different 

 in different people and may vary in one and the same individual, it 

 follows that the amount of urea also must vary. Any figures indi- 

 cating the amount of urea that is eliminated in the urine can there- 

 fore be of little value unless we are acquainted with the actual state 

 of health of the individual, his body-weight, his habits of life as 

 regards exercise, the amount of nitrogenous food ingested, etc. 

 Having a knowledge of all these factors, however, we may be able 

 to say whether the amount of urea is normal or not. Certain figures 

 have' been given by physiologists to indicate the amount of nitrogen- 

 ous food which should enter into the composition of the diet, and 

 from these we can approximately calculate the amount of urea that 

 should appear in the urine. By estimating this in turn, or still 

 better, of course, the total amount of nitrogen, we can accordingly 

 decide whether or not the individual is consuming a sufficient amount 

 of nitrogen in his food. The figures, however, have been constructed 

 without "due regard to the factors above indicated, and are in my 

 opinion, at least, too high as averages. 



I am willing to admit that an elimination of 40-50 grammes of 

 urea may be normal in certain cases, as in soldiers on forced marches, 



