342 CHEMIOAL DISCOVERY AND INVENTION 



there are no cases in which complete knowledge has been yet 

 achieved except in regard to the bases found in tea and cocoa, 

 to which reference has already been made. 



The complete synthesis of such an alkaloid as quinine, strych- 

 nine, or morphine will doubtless be accomplished in the not far 

 distant future, but at present all that can be put forward in such 

 a case is a tentative expression which embodies more or less 

 completely the results of operations in which the molecule is 

 broken up into recognisable parts. The solution of problems of 

 this kind is, however, less important from one point of view than 

 was formerly th'e case. For physiologists have learnt to make 

 use of chemistry more freely than in earlier times, and, as already 

 mentioned, a large number of laboratory products are now at 

 the disposal of the physician, which make the ordinary practice 

 of medicine to some extent independent of the supply of natural 

 drugs. Probably this tendency will continue to be developed 

 until in time chemical constitution and physiological action will 

 be so completely correlated that the requirements of medicine 

 will be immediately supplied by the chemical laboratory. 



CHAPTER XXIII 



PERFUMES AND ESSENTIAL OILS 



FROM drugs we may pass by an easy transition to perfumes and 

 flavouring materials. It was among these things that one of the 

 earliest triumphs of synthetical chemistry was celebrated when 

 Perkin, the discoverer of the first coal-tar dye, contrived a process 

 by which salicylic aldehyde could be transformed into coumarin. 

 This was in 1S68, and since a method was found in 1876 by 

 which salicylic aldehyde could be produced from phenol, the 

 synthesis may be regarded as complete, for, if necessary, phenol 

 can be made from benzene, and benzene from acetylene, and the 

 last can be formed by uniting carbon and hydrogen. 



Coumarin is the fragrant substance to which the perfume of 

 the Tonquin bean, of woodruff, and some other plants is due, 

 and artificial coumarin is now an article of manufacture without 

 the aid of the plant. 



It was not long before a second step of the same kind was 

 taken, for in 1876 a method was discovered for the synthesis of 

 vanillin, the sweet-smelling constituent of the vanilla pod, so 



