i8o 



BIOLOGICAL CHEMISTRY 



in birds and reptiles as the osmotic pressure cannot rise above 

 that of a saturated solution. The greater the osmotic pressure 

 the greater the work done by the kidney in separating the 

 excretion. 



On the other hand, insoluble substances in mammalian urine 

 would lead to precipitates and concretions which would 

 irritate the urinary passages. 



TABLE XXXIV 



Showing average composition of urine from different types of 

 animals in grams per litre* 



In what follows we shall consider chiefly the relations of 

 the various substances in human urine. The same principles 

 apply to other animals, but slight differences occur owing to 

 differences in the end products. The excretion of inorganic 

 salts requires no further notice as their amounts are dependent 

 on the amount of the salts in the food, except in disease, when 

 retention of salts may occur. The specific gravity varies 

 according to the relative amounts of liquid and solid to be 

 removed from the body. In normal human urine the specific 

 gravity varies between 1-015 and 1-025. 



REACTION OF URINE 



The reaction of the urine depends upon various conditions. 

 In carnivora the reaction is predominantly acid and in 

 herbivora alkaline. This difference is due to the excess of 

 alkaline salts in the food of herbivora. The reaction of the 

 urine reflects the reaction of the blood, as the kidney is the 



* A. Ellinger, Oppenheimer's Handbuch d. Biochemie, 1910, vol. 3, 

 part i, p, 543. 



