i^OVEMBEB 25, 1910] 



SCIENCE 



741 



tivities of the organs to which they are 

 related. It is at least conceivable that 

 agencies which produce chemical disturb- 

 ances in the circulating fluids may alter the 

 chemical constitution of the hormones, and 

 thus produce far-reaching effects. The 

 pathology of the thyroid gland gives some 

 ground for belief that such changes may 

 be produced by the action of external con- 

 ditions. But, however this may be, the line 

 of reasoning that we have followed raises 

 the expectation that a chemical bond must 

 exist between the functionally active or- 

 gans of the body and the germ-cells. For 

 if, in the absence of a specialized nervous 

 system, the only possible regulating and 

 eoadapting mechanism is a chemical mech- 

 anism, and if the specific activities of a cell 

 are dependent on the enzymes which it 

 holds in combination, the germ-cells of any 

 given animal must be the depository of a 

 stock of enzymes sufficient to insure the 

 due succession of all its developmental 

 stages as well as of its adult structure and 

 functions. And as the number of blasto- 

 meres increases, and the need for coordi- 

 nation of form and function arises, before 

 ever the rudiments of a nervous system are 

 differentiated, it is necessary to assume 

 that there is also a stock of appropriate 

 hormones to supply the chemical nexus be- 

 tween the different parts of the embrj'-o. 

 The only alternative is to suppose that they 

 are synthesized as required in the course of 

 development. There are grave objections 

 to this supposition. All the evidence at 

 our disposal goes to show that the poten- 

 tialities of germ-cells are determined at the 

 close of the maturation divisions. Follow- 

 ing the physiological line of argument, it 

 must be allowed that in this connection 

 "potentialit}'" can mean nothing else 

 than chemical constitution. If we admit 

 this, we admit the validity of the theory 

 advanced by more than one physiologist 



that heritable "characters" or "tenden- 

 cies" must be identified with the enzymes 

 carried in the germ-cells. If this be a true 

 representation of the facts, and if the most 

 fundamental and primitive bond between 

 one part of an organism and another is a 

 chemical bond, it can hardly be the case 

 that germ-cells — which, inter alia, are the 

 most primitive, in the sense of being the 

 least differentiated, cells in the body — 

 should be the only cells which are exempt 

 from the chemical influences which go to 

 make up the coordinate life of the organ- 

 ism. It would seem, therefore, that there 

 is some theoretical justification for the in- 

 heritance of induced modifications, pro- 

 vided that these are of such a kind as to 

 react chemically on the enzymes contained 

 in the germ-cells. 



One further idea that suggests itself to 

 me and I have done. Is it possible that dif- 

 ferent kinds of enzymes exercise an in- 

 hibiting influence on one another; that 

 germ-cells are "undifferentiated" because 

 they contain a large number of enzymes, 

 none of which can show their activities in 

 the presence of others, and that what we 

 call "differentiation" consists in the segre- 

 gation of the different kinds into separate 

 cells, or perhaps, prior to cell-formation, 

 into different parts of the fertilized ovum, 

 giving rise to the phenomenon known to us 

 as prelocalization ? The idea is purely 

 speculative; but, if it could be shown to 

 have any warrant, it would go far to assist 

 lis in getting an understanding of the laws 

 of the production of form. 



I have been wandering in territories out- 

 side my own province, and I shall certainly 

 be told that I have lost my way. But my 

 thesis has been that morphology, if it is to 

 make useful progress, must come out of its 

 reserves and explore new ground. To ex- 

 plore is to tread unknown paths, and one is 

 likely to lose one's way in the unknown. 



