422 VETERINARY PHYSIOLOGY 



The pigment which gives the pink colour to urates has been 

 called uroerythrin, and its chemical nature is unknown. 



Hsematoporphyrin (see p. 213) is normally present in small 

 traces in the urine, but in certain pathological states it is 

 increased in amount and gives a brown colour to the urine. 



VII. Nueleo-protein 



A mucin-like nucleo-protein derived from the urinary passages 

 is always present in small amounts, and forms a cloud when the 

 urine stands. 



VIII. Carbonic and Oxalic Acids 



1. Carbonic Acid. Small amounts of this are present m 

 urine of carnivores. 



In herbivora it is present in large amounts, combined with 

 potassium, lime, and magnesia, and also free. The carbonate 

 of lime readily crystallises out in large dumb-bell-like crystals 

 which may be confused with crystals of oxalate of lime, but 

 which are quickly soluble, with effervescence, on the addition 

 of an acid. 



The differences between the urines of different herbivora are 

 not important. The urine of the ox and cow is more abundant 

 and more dilute than the urine of the horse, while the urine of 

 the sheep is considerably more concentrated and contains a 

 very high proportion of hippuric acid. 



2. Oxalic acid 







il II 

 H C C H 



is a substance in a stage of oxidation just above that of carbonic 

 acid. It is frequently present in the urine linked with lime, 

 and the lime salt tends to crystallise out in characteristic 

 octohedra, looking like small square envelopes under the micro- 

 scope. Under certain conditions these crystals assume other 

 shapes. The oxalic acid of the urine is chiefly derived from 

 oxalates in vegetable foods, but it has been detected in the 

 urine of animals on a purely flesh diet. 



