200 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1916. 



have broken up all the organic molecules, who have identifiod the 

 constructive plan of these minute edifices, have been urged on by two 

 other motives of a far more immediate import. 



The first motive is the attractiveness of synthesis. It is acknowl- 

 edged that the artificial reproduction of a natural compound can 

 be brought about only when the composition of that natural com- 

 pound is known in its minutest details. Whenever an attempt is 

 made to proceed in any other way, to put the cart before the horse, 

 as they say, and to work haphazard, the result is invariably a failure. 

 The latest example of this is the fruitless attempts to make artificial 

 rubber. 



In the second place chemists have given their close attention to 

 (questions of composition because they are not slow to recognize the 

 fundamental fact that all the properties of organic compounds — 

 physical, chemical, and physiological — stand in intimate relation 

 to this composition. It is not the quantity nor the nature of the 

 materials employed in the construction of a building that makers of 

 it a church, a theater, or a railway station. In the siime way it is 

 neither the specific kind nor the number of the atoms of a molecule 

 that makes of an organic compound a coloring material, an anti- 

 septic, or a perfume; it is simply the way in which the atoms are 

 grouped one with the other. To know this method of grouping will 

 be to possess the means of preparing at will and at one stroke any 

 given new compound with predetermined properties. 



A mass of relations of the highest interest between the composi- 

 tion and certain properties of substances have thus been established, 

 such as their color, their staining quality, their density, their flavor, 

 their polarization, their therapeutic action, etc. But all branches 

 of this study have not been explored; in particular, no attempt has 

 yet been made to connect their biological properties with the struc- 

 ture of molecules. 



This is the subject that I should like to discuss at this time, and I 

 begin by limiting it to the three following questions : 



(1) Is there a relation between the chemical composition of a 

 substance and the part it plays in the interior of a living organism ? 



(2) Is there a condition of molecular structure which makes a 

 substance useful, inactive, or harmful in sustaining life, which 

 makes it a food or a poison? 



(3) Is there a like condition by which the material of a living 

 cell is distinguished from that of the same cell when dead ; in other 

 words, does death result in changing the architecture of the mole- 

 cules? 



Before answering these questions it seems desirable to specify 

 clearly with what particular phase of the theory of constitution my 

 discussion will have to do and be assured I shall limit myself to 



