The Various Substances Made by Plants 137 



tory. It seems quite plain, however, that the role of these 

 elements lies in services incidentally necessary to the greater 

 processes, such as aiding in chemical steps, neutralizing poison- 

 ous excretions, and so forth. They are like the servants at a 

 party; they are indispensable to its success, but their names do 

 not appear in the list of those present. But our ignorance on 

 these matters, and upon so many other phases of our subject of 

 metabolism, is only acting as a spur to the efforts of many de- 

 voted workers, who, in laboratories all over the world, are attack- 

 ing these problems with the full determination to solve them. 

 The methods of science are slow, but they are irresistible; and 

 the solution of the problems is only a matter of time. 



