416 VETERINARY PHYSIOLOGY 



are apt to get into it, and to cause a hydration of the urea, 

 whereby it is changed into ammonium carbonate 



HI H 



H, N ,H 



H 



\N C N/ Hr~ ~" H 



H 



II 



The urine if acid is thus made alkaline, and in carnivora 

 the phosphates of the earths are precipitated. The phosphate 

 of magnesium combines with the ammonia to form ammonio- 

 magnesium-phosphate, NH 4 MgP0 4 + 6H 2 O, which crystallises 

 in characteristic prism-like crystals. In the horse and other 

 herbivora it is the carbonate of lime which is precipitated. 



B. Non-Urea Nitrogen. The 10 to 20 per cent, of nitrogen 

 which on an ordinary diet is not excreted as urea is dis- 

 tributed in : 



1. Ammonium Salts. About 4 or 5 per cent, of the total 

 nitrogen is normally excreted as ammonium salts in the dog, 

 but in the horse the proportion is much smaller. But under 

 certain conditions the proportion is greatly increased. Any- 

 thing which causes an increased breaking down of protein 

 and an increased formation of acids in carnivora, leads to an 

 increased excretion of ammonia the ammonia being formed 

 from the proteins to neutralise the acids. 



2. Diureides. The members of this series of bodies consist 

 of two unmodified or modified urea molecules, linked together 

 by an acid nucleus. The most important of the series have 

 acrylic acid as the linking molecule, and they constitute 

 the purin bodies. 







II 



H N C 



! I 



O= C C N H v 



| II >C = 



H N C N W 



In birds and. reptiles they replace urea as the substances 

 in which nitrogen is chiefly eliminated. In these animals 



