THE URINE. 297 



and tortoise is also destitute of urea, but does not contain urate of ammonia so 

 pure. That of the frog and toad contains urea, chloride of sodium, and a little 

 phosphate of lime. 6 The urine of fish, as well as of birds and reptiles, and the 

 kidneys of mollusca, contain uric acid. f In oviparous animals the urine is formed 

 from venous blood, the kidneys having a double venous circulation, exactly as is 

 the case with the human liver. g 



The urine of carnivorous mammalia contains uric acid and urea ; while that 

 of herbivorous brutes contains uro-benzoates and urea, but no uric acid, and is 

 generally deficient in phosphates, which are replaced by carbonates. 



e Consult Berzelius, 1. c. f Ibid. 



g Dr. Jacobson, De system, venos. peculiari in permultis animalibus observato* 

 Hafnise, 1821 j and Edinb. Med. and Surg. Journ. vol.xix. p. 78. 



