142 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1934 



a long chain as in vitamin A they are united into a system of con- 

 densed rings. Similar rings form the basal component of the mole- 

 cules of sterols, substances which are normal constituents of nearly 

 every living cell. It is one of these, inactive itself, which ultra- 

 violet radiation converts into vitamin D. We know that as stated 

 each of these vitamins stimulates growth in tissue cells. Next con- 

 sider another case of growth stimulation, diiferent because patho- 

 logical in nature. As you are doubtless aware, it is well known that 

 long contact with tar induces a cancerous growth of the skin. Very 

 important researches have recently shown that particular constit- 

 uents in the tar are alone concerned in producing this effect. It is 

 being further demonstrated that the power to produce cancer is 

 associated with a special type of molecular structure in these con- 

 stituents. This structure, like that of the sterols, is one of condensed 

 rings, the essential difference being that (in chemical language) the 

 sterol rings are hydrogenated, whereas those in the cancer-producing 

 molecules are not. Hydrogenation indeed destroys the activity of 

 the latter. Kecall, however, the ovarian hormone oestrin. Now the 

 molecular structure of oestrin has the essential ring structure of a 

 sterol, but one of the constituent rings is not hydrogenated. In a 

 sense therefore the chemical nature of oestrin links vitamin D with 

 that of cancer-producing substances. Further, it is found that sub- 

 stances with pronounced cancer-producing powers may produce 

 effects in the body like those of oestrin. It is difficult when faced 

 with such relations not to wonder whether the metabolism of sterols, 

 which when normal can produce a substance stimulating physiolog- 

 ical growth, may in very special circumstances be so perverted as to 

 produce within living cells a substance stimulating pathological 

 growth. Such a suggestion must, however, with present knowledge, 

 be very cautiously received. It is wholly without experimental 

 proof. My chief purpose in this reference to this very interesting 

 set of relations is to emphasize once more the significance of chemical 

 structure in the field of biological events. 



Only the end results of the profound influence which minute 

 amounts of substances with adjusted structure exert upon living cells 

 or tissues can be observed in the intact bodies of man or animals. 

 It is doubtless because of the elaborate and sensitive organization of 

 chemical events in every tissue cell that the effects are proportionally 

 so great. 



It is an immediate task of biochemistry to explore the mechanism 

 of such activities. It must learn to describe in objective chemical 

 terms precisely how and where such molecules as those of hormones 

 and vitamins intrude into the chemical events of metabolism. It is 

 indeed now beginning this task which is by no means outside the 

 scope of its methods. Efforts of this and of similar kind cannot 



