General Scope of Biochemical Study. 9 



urine of animals (by Fourcroy and Vauquelin in 1799), 

 and was regarded as a typical product of vital origin ; this 

 was actually obtained from materials which had been 

 hitherto regarded as inorganic. The discovery of Wohler 

 was not immediately followed up by many other artificial 

 constructions of organic substances, but in the later de- 

 velopments of organic chemistry the " synthetical " method 

 has proved the most useful one in the determination of 

 the structure or constitution of organic compounds. 



It can be readily understood that a knowledge of the 

 structure of plant and animal products was necessary 

 before any real advance could be made in the study of 

 the methods by means of which such substances could be 

 formed or utilized by living objects. A great pioneer in 

 this branch of investigation was Liebig, who, by the pub- 

 lication of three great works, created an epoch in the 

 study of biological chemistry. The three works in ques- 

 tion were entitled, " Chemistry in its Application to Agri- 

 culture and Physiology," 1840; "Animal or Organic 

 Chemistry in its Application to Physiology and Pathol- 

 ogy/' 1842; and "The Chemical Processes in the Nutri- 

 tion of Vegetables and the Natural Laws of Tillage," 

 1862* 



From the foregoing remarks it will be observed that 

 there are three stages in the biochemical study of any 

 given substance. In the first place, it is necessary to 

 isolate it in a state of purity and unmixed with other 

 substances from the animal or plant in which it has been 

 produced ; in the second place, its chemical structure or 

 " constitution " must be determined ; and in the third 

 place, the method by means of which it is built up or 

 broken down in the organism must be investigated. The 

 process of change of chemical substances in the organism 



* English translations are given of the original German titles. 



