RENAL SECRETION. 637 



food and drink, partly from modifications of the vegetable. acid com- 

 pounds in vegetable foods. 



The urea and uric acid are the nitrogenous end products of the 

 decomposition of the albuminoids of food and of the tissues. 



Kreatin and kreatinin are closely dependent on the animal matter 

 taken as food, since, even in muscle, kreatin is formed as a modification 

 of its own albuminoid constituents. 



Hippuric acid is a combination of glyeochol with benzoic acid, and 

 originates, to a great extent, in the constituents of vegetable foods, the 

 cuticular substance of which develops the benzoic acid. 



' Phenol is derived from the decomposition of albuminoids in the 

 intestine, and in the excretory ducts of the kidney unites with H 2 S0 4 . 



Indican originates in indol. 



Many other substances are accidentally present in urine, such as 

 aromatic constituents of food, alkaloids, metals, bile coloring-matter, etc. 



The quantity of the urine is dependent on the amount of water 

 taken in food and drink, on the diminution of excretion of water by 

 other organs, especially the skin, on the amount of excretory products, 

 especially urea, and on the amount of substances taken in food, e.g., 

 salts, which must be excreted. 



It is to be noted that all the water taken as food is not excreted 

 through the kidneys, but that part is removed by the lungs, skin, and 

 intestinal canal. The proportion of water removed through these 

 different organs varies in different species : — 



In the Urine. Through the Lungs. 

 In herbivora, 20 per cent, of water is removed; 80 per cent. 



In omnivora, 60 " " " 40 



In carnivora, 85 " " " 15 " 



Various conditions rmiy, however, modify these proportions. 



In fasting and suckling animals of both the herbivora and carnivora 

 the urine has the same characters, since in them the tissues alone are 

 undergoing waste. 



There is the greatest difference between the urine of carnivora and 

 herbivora. 



In carnivora the urine is smaller in amount, is acid, clear, and richer 

 in solids, especially urea, uric acid, and kreatin; sodium salts, sulphates, 

 and phosphates are in excess, and the urine has a higher specific gravity. 

 Phenol and sulphuric acid only are present in small amount and hippuric 

 acid absent when on a purely flesh diet. 



In herbivora it is larger in amount, is turbid, contains few solids, 

 hippuric acid replaces uric acid, and the reaction is alkaline ; urea is 

 present only in small amount. Potassium salts are in excess' unless 

 sodium chloride is given with the food. Lime and magnesium, united 

 with C0 2 , are in abundance, phosphates often absent, sulphates abundant. 



