THE URINE 331 



colour to the stale urine of the horse. In the dog glycuronic 

 acid may be united to some of the skatol and phenol, and this 

 substance exercises a reducing action on salts of copper, which 

 might be mistaken for dextrose. 



In man and the dog the ethereal sulphates are regarded as 

 a measure of protein disintegration, but in the horse this is not 

 so. Salkowski showed that in the urine of the horse 18 -8 grammes 

 of total sulphates were excreted, of which no less than 

 10 3 grammes belonged to the group of ethereal sulphates. 



The colouring matter of the urine is a question not fully settled. 

 There are known to be several pigments, the chief one being 

 urochrome, which is probably an oxidation product of urobilin. 

 Urobilin is formed from stercobilin, which is absorbed from the 

 intestinal canal. The mother-substance of urobilin is a chromogen, 

 which yields urobilin on oxidation. 



The Inorganic Substances found in the urine are calcium, 

 magnesium, sodium, and potassium, existing in the form of 

 chlorides, sulphates, phosphates, and carbonates. The origin 

 of these salts is from the food taken into the body, but mainly 

 from metabolic processes occurring in the tissues. The nature 

 and amount of the salts varies with the class of animal and the 

 character of the food. In the urine of the horse potassium salts 

 predominate, sodium and magnesium are present in small 

 amounts, phosphates are practically absent, while sulphates and 

 chlorides are in considerable quantity. It has been found that 

 in ruminants the calcium salts are mostly excreted with the 

 faeces, whereas in the horse they principally pass through the 

 kidneys. It is certain that phosphates, which form such a 

 prominent feature in the urine of carnivora and omnivora, are 

 in the horse almost wholly excreted by the intestines. 



Calcium. — More lime exists in the urine of the horse than is 

 soluble in an alkaline 'fluid, so that both suspended and dissolved 

 lime exists ; the former increases with the age of the urine, 

 owing to the development of ammonia, until nearly the whole 

 of the lime is precipitated. The lime exists in combination with 

 oxalic, carbonic, hippuric, and sulphuric acids ; all these com- 

 binations do not necessarily exist in one specimen of urine, the 

 salts formed depending on the varying relative amounts of the 

 acids formed in metabolism. The amount of lime in the food 

 does not influence the elimination through the kidneys, but 

 more lime is found in the urine of horses at work than of those 

 at rest. Oxalate and carbonate of lime crystals are common 

 microscopic deposits in the urine of the horse (Figs. 102 and 103) . 

 The oxalic acid is derived from the oxalate contained in the 

 vegetable substances of the food. 



The turbidity of the healthy urine of the horse is due to sus- 



