UKINE 151 



formed directly or by the breakdown of amino-acids, is the principal 

 immediate precursor of urea. 



The following structural formulae show the relationship between 

 ammonium carbonate, ammonium carbamate, and urea : 



_ r /O.NH 4 _ r /NH 2 _ r /NH 2 



" 



[ammonium carbonate] [ammonium carbamate] [urea or carbamide] 



The loss of one molecule of water from ammonium carbonate pro- 

 duces ammonium carbamate ; the loss of a second molecule of water 

 produces urea, 



AMMONIA 



The urine of man and carnivora contains small quantities of 

 ammonium salts. The reason that some ammonia always slips 

 through into the urine is that a part of the ammonia-containing 

 blood passes through the kidney before reaching organs, such as the 

 liver, which are capable of synthesising urea. In man the daily 

 amount of ammonia excreted varies between 0*3 and 1'2 gramme : 

 the average is 0*7 gramme. The ingestion of ammonium carbonate 

 does not increase the amount of ammonia in the urine, but increases 

 the amount of urea, into which substance the ammonium carbonate 

 is easily converted. But if a more stable salt, like ammonium 

 chloride, is given, it appears as such in the urine. 



Under normal circumstances the amount of ammonia depends on 

 the adjustment between the production of acid substances in meta- 

 bolism and the supply of bases in the food. Ammonia formation is 

 the physiological remedy for deficiency of bases. 



When the production of acids is excessive (as in diabetes), or 

 when mineral acids -are given by the mouth or injected into the 

 blood-stream, the result is an increase of the physiological remedy, 

 and excess of the ammonia passes over into the urine. Under normal 

 conditions ammonia is kept at a minimum, being finally converted 

 into the less toxic substance urea, which the kidneys easily excrete. 

 The defence of the organism against acids which are very toxic is an 

 increase of ammonia formation, or, to put it more correctly, less of 

 the ammonia formed is converted into urea. 



Under the opposite conditions namely, excess of alkali, either in 

 food or given as such the ammonia disappears from the urine, all 

 being converted into urea. Hence the diminution of ammonia in the 

 urine of man on a vegetable diet, and its absence in the urine of 

 herbivorous animals. 



Not only is this the case but if ammonium chloride is given to a 



