264 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 30 



tetrachloride. As carbon tetrachloride is practically transparent in 

 this region, all frequencies of the range are present in considerable 

 strength. The second curve shows the effect of adding 0.127 grams 

 of paradichlorbenzene. Here it will be noticed that frequencies in 

 the region of 1.13/i, and 1.66ju, are much weaker, those being the char- 

 acteristic frequencies absorbed by the paradichlorbenzene. The other 

 curves show successively greater concentrations of paradichlorbenzene. 

 It will be noticed that the weaker absorption frequencies are more 

 clearly evident in the greater concentrations. By comparing the 

 characteristic frequencies absorbed in paradichlorbenzene with other 

 halogen derivitives of benzene, important information can be gained 

 in regard to the structure of these interesting molecules. This 

 type of study will eventually be extended to molecules which are of 

 importance in the biological processes. 



While it is possible, through direct observation of complicated 

 living organisms, to accumulate a vast amount of valuable informa- 



1.4- IS re t.7 



FiGUEB 2. — Absorption spectrum of paradichlorbeuzene 



tion, complete understanding of the processes which are involved 

 is impossible without a knowledge of the structure and characteristics 

 of the molecules entering into these processes. Most of the molecules, 

 such as those of chlorophyll, the various proteins, and enzymes, are so 

 complicated as to render it impossible to gain even the customary 

 chemical knowledge derived from analysis and synthesis. Keal un- 

 derstanding requires not only this information, but a knowledge of 

 other phj'^sical characteristics which determine the nature of their 

 chemical reactions and their responses to various wave lengths of 

 light. The most logical hope of progress in studying these very com- 

 plicated molecules is to bring to bear those methods which yield the 

 greatest amount of independent data. The type of investigation 

 just described is one of the most promising approaches which has 

 offered itself. Thus these types of research which, at first glance 

 seem remote from biology, should, in the long run, prove of the 

 greatest value in gaining a fundamental understanding of these 

 biological processes which are of such vital importance. 



