UREA. 427 



blood it is finally removed by the kidneys, principally in 

 the form of urea and uric acid, and thrown off as waste 

 material from the system. These substances, although 

 organic, may be figuratively regarded as the ashes of 

 the consumed muscle and other nitrogenous constitu- 

 ents of the body. A portion of the carbon and hy- 

 drogen of the animal organs has at the same time dis- 

 appeared, like the elements of respiratory food, in the 

 form of water and carbonic acid. 



What is 1061. UREA. Urea, when " separated 



said of Urea ? f rO m its solution, is obtained as a white 

 crystalline solid. Its molecule contains four atoms of 

 hydrogen, to two each of carbon, nitrogen, and oxygen. 

 When left in contact with the mucus with which 

 it is accompanied in the secretion of the kidneys, 

 it is speedily converted, by combination with four 

 molecules of water, into carbonate of ammonia. Urea 

 may also be artificially produced from cyanic acid arid 

 ammonia. This cyanate is identical with urea in 

 composition, and is converted into urea by solution in 

 water and evaporation. It was among the first of 

 organic bodies artificially produced. Uric acid con- 

 tains the same elements with a larger proportion of 

 oxygen, and also yields ammonia by its decomposition. 

 Besides the above substances, the secretion of the kid- 

 neys contains various soluble salts, which have formed 

 part of the body. The insoluble salts are removed 

 from the system by other means. 



1062. DISAPPEARANCE OF FAT. STARVA- 



What is said 



of the disap- TioN. Vv hen the supply oi respiratory 



P nce f food is deficient, nature avails herself of 



the fat previously stored in the animal 



