THE GROWTH OF CHEMICAL IDEAS 129 



molecules of the substance together to form chains or net- 

 works of molecules, producing compounds having high mo- 

 lecular weights. Such compounds have long been known in 

 nature; molecules of sugar, for instance, polymerize to form 

 starch and cellulose. By this means, chemists have built up 

 a large group of so-called plastics— comY>ounds having a high 

 molecular weight and usually valuable properties comparable 

 with those of the natural products that have been of such 

 value to man throughout the ages, such as wood, wool, cotton, 

 and glass. The study of the plastics and of high-molecular 

 compounds generally is now a very important branch of 

 chemistry, and the ideas involved in the structure of polymers 

 are coming to the front in modern chemical theory. 



The chemical reactions that occur in living organisms have 

 been studied primarily by chemical physiologists, and the 

 determination of the nature of some of the simpler of these 

 reactions will be discussed in the next chapter (page 169). 

 The identification of some of the compounds formed and 

 their synthesis in the laboratory have, however, been among 

 the triumphs of organic chemistry, which, indeed, owes its 

 very name to this field of work. The nitrogen-containing 

 compound urea was identified by von Liebig in the blood and 

 urine of mammals, in which it is the chief vehicle for the 

 elimination of the nitrogen produced by the katabolism of 

 the proteins. In 1828 Wohler synthesized urea, an event 

 that aroused great interest and some controversy since urea 

 had been considered a typical product of "vital" processes. 

 After von Liebig, the greatest name in this field of chemistry 

 is Emil Fischer, who, after acting as assistant to Adolf von 

 Baeyer at Munich, became professor of chemistry successively 

 at Erlangen, Wiirzburg, and Berlin. While studying deriva- 

 tives of hydrazine, he discovered that phenylhydrazine reacts 

 with sugars to form well-crystallized compounds, osazones. 

 Then he turned his attention to nitrogen-containing com- 

 pounds related to uric acid and showed that all of them 

 were derived from a base, purine, which he synthesized, wdth 

 many of its derivatives. Then he returned to the study of 



