394 STUDIES IN ADVANCED PHYSIOLOGY. 



boratory. In 1828 the chemist Wohler discovered that by 

 allowing a solution of ammonium cyanate (NH 4 CON) to 

 stand exposed to the air it changed into urea CO (NH 2 ) 2 . 



It will be noticed in comparing the chemical composi- 

 tions of these two substances that they have the same rela- 

 tive number of atoms. Urea is, therefore, but a re-arrange- 

 ment of the molecular structure of ammonium cyanate. It 

 was, of course, easy to make ammonium cyanate out of its 

 elements in the laboratory, and so it became possible to 

 make urea artificially in the chemist's retorts. Before this 

 time it had been believed without question that all organic 

 compounds, that is, compounds made by plants or animals, 

 differed essentially from compounds made artificially. It 

 was believed that in the construction of organic compounds 

 vital forces were at work in addition to chemical affinities. 

 This wonderful discovery at once showed the error of this 

 view and opened the way for the increased study of organic 

 compounds and for the artificial manufacture of innumera- 

 ble ones now on the markets. It was the first blow to break 

 down the distinction between organic and inorganic chem- 

 istry. 



This urea may be extracted from tne secretion in a pure 

 solid form. It crystallizes in white four-cornered prisms, or 

 when crystallized very rapidly, in fine needles. The solid 

 crystals are soluble in water, alcohol, and many other solu- 

 tions, but are perfectly insoluble in ether. 



If a solution containing urea be allowed to stand for some 

 time exposed to the air, it ferments under the action of 

 germs falling into it from the air, and the urea uniting 

 chemically with some of the water changes into ammonium 

 carbonate. This change is called the fermentation of the urea. 

 Ammonium carbonate, more familiar as the salts of harts- 

 horn, has its peculiar characteristic odor, and it is to this 

 substance that the odor of fermented urine is due. 



The derivatives of urea, such as uric acid, kreatin, xan- 

 thin and others, are found in relatively small amounts. Under 

 certain conditions, however, the uric acid may accumulate 



