3?< 6 



A MANUAL OF VETERINARY PHYSIOLOGY 



the food, or from the tissues, as we have seen is the case with 

 urea. In man food rich in nuclein, such as thymus, pancreas, 

 and herring roe, and in purin bases as meat extract, increases 

 the amount of uric acid produced. Uric acid (Fig. 98) does not 

 exist in the urine in a free state, but as urates of soda or potash. 

 Two classes of urates are formed — normal and acid. The acid 

 sodium urate is the chief constituent of the reddish deposit of 

 urates which occurs in acid urines. 



We have referred to purin bases as bodies, and a word in ex- 

 planation is necessary. Purin is the name given by E. Fischer 

 to the nucleus common to the uric acid group of substances, 



from which, by transforma- 

 tions, several members of 

 the group may easily be 

 obtained. 



The purin group consists 

 of the following bases : 



f Xanthine. 

 Purin IHypoxanthine. 

 Bases. 1 Adenine. 



I Guanine. 



And from these uric acid 

 may be formed probably by 

 the following process : Under 

 the influence of ferments the 

 nuclein is split off from the 

 protein and acted upon by 

 a tissue enzyme known as 

 nuclease. This splits the nuclein, and results in the formation 

 of the above-named purin bases. Adenine and guanine, under 

 the influence of ferments, are converted into hypoxanthine and 

 xanthine, and these bodies, on being acted upon by an oxidase 

 ferment, are oxidised to uric acid. 



Oi the uric acid so formed a portion under the influence of 

 a urolytic ferment is, as previously noted, converted into urea. 



Trie uric acid problems have been worked out mainly on the 

 dog, apart from what has been done on birds. In the case of 

 the non-suckling herbivora, it is known that in a condition of 

 health uric acid is not found, or only to a trifling extent. It 

 is present in the suckling, also in the adult, immediately the 

 animal begins to live on its own tissues, as in disease. It appears 

 clear that a flesh diet, especially of cellular organs such as the 

 various glands, favours its production, while a vegetable one 

 either inhibits its formation or else destroys it, perhaps in the 

 liver, under the influence of a body ferment, and urea produced. 

 This is pure conjecture. The question of the production of uric 



F;g. 98. — Crystals of Uric Acid (Funke). 



