CHEMICAL ASPECTS OF LIFE HOPKINS 145 



This is assuredly true of the data which biochemistry is now acquir- 

 ing. Never during its progress has chemical consistency shown 

 itself to be disturbed by influences of any ultrachemical kind. 



Moreover, before we assume that there is a level of organization 

 at which chemical controlling agencies must necessarily cease to 

 function, we should respect the intellectual parsimony taught by 

 Occam and be sure of their limitations before we seek for super- 

 chemical entities as organizers. There is no orderly succession of 

 events which would seem less likely to be controlled by the mere 

 chemical properties of a substance than the cell divisions and cell 

 differentiation which intervene between the fertilized ovum and the 

 finished embryo. Yet it would seem that a transmitted substance, 

 a hormone in essence, may play an unmistakable part in that 

 remarkable drama. It has for some years been known that, at an 

 early stage of development, a group of cells forming the so-called 

 " organizer " of Spemann induces the subsequent stages of differentia- 

 tion in other cells. The latest researches seem to show that a cell- 

 free extract of this " organizer " may function in its place. The sub- 

 stance concerned is, it would seem, not confined to the " organizer " 

 itself, but is widely distributed outside, though not in, the embryo. 

 It presents, ncA-ertheless, a truly remarkable instance of chemical 

 influence. 



It would be out of place in such a discourse as this to attempt 

 any discussion of the psychophysical problem. However much 

 we may learn about the material systems which, in their integrity, 

 are associated with consciousness, the nature of that association may 

 yet remain a problem. The interest of that problem is insistent 

 and it must be often in our thoughts. Its existence, however, 

 justifies no prejudgments as to the value of any Icnowledge of a 

 consistent sort which the material systems may yield to experiment. 



It has become clear, I think, that chemical modes of thought, 

 whatever their limitation, are fated profoundly to affect biological 

 thought. If, however, the biochemist should at any time be inclined 

 to overrate the value of his contributions to biology, or to under- 

 rate the magnitude of problems outside his province, he will do well 

 sometimes to leave the laboratory for the field, or to seek even in the 

 museum a reminder of that infinity of adaptations of which life is 

 capable. He will then not fail to work with a humble mind, however 

 great his faith in the importance of the methods which are his own. 



It is surely right, however, to claim that in passing from its 

 earlier concern with dead biological products to its present concern 



