362 PHILOSOPHY OF ZOOLOGY. 



the same ingredients are found as in that of man In all, 

 urea exists, but the nature and proportion of the acids, al- 

 kalis, and earths which are present, are somewhat different. 

 Thus, in the gramenivorous animals, there is no uric acid, 

 while the benzoic acid is present in such quantity, as to al- 

 low of its being extracted for commercial purposes. The 

 phosphoric acid and its combinations, are likewise absent in 

 the urine of many quadrupeds. 



Urea, and uric acid, appear therefore to be substances 

 peculiar to urine, and as they have not been detected ready 

 formed in the blood, it appears reasonable to conclude, that 

 they are produced by the kidneys. 



The contents of the urine in the same individual, appear 

 to differ with age, food, or disease. In infants, there is no 

 phosphoric acid, and but feeble traces of uric acid ; while 

 in adults, both uric acid and earthy phosphats abound. A 

 variety of substances, such as nitre, alkalis, carbonic acid, 

 rhubarb, or madder, when taken into the stomach, com- 

 municate their sensible qualities to the urine in a very re- 

 markable manner, leading some to believe, that there is a 

 passage for fluids from the stomach to the kidneys, inde- 

 pendent of the ordinary course of circulation. 



But, the most singular changes which take place in urine 

 are effected by disease. In diabetes, the quantity is increased 

 in a great degree, as well as its density. The proportion of 

 urea his diminished to such an extent, that it can with 

 difficulty be detected, while sugar occupies its place in 

 abundance. These two substances contain the same ele- 

 ments, but in different proportions. While the hydrogen 

 of the urea remains the same, its azote disappears, and the 

 quantity of carbon and oxygen being doubled, produces 

 the sugar. Mr Rose has likewise remarked the absence of 

 urea in the urine of patients, labouring under chronic and 



