1899] REGENERATION 327 



my explanations were not satisfactory even to myself, I can only give 

 the simple reason that the fundamental basis of the theory appeared 

 to me useful, and a fully worked-out theory seemed necessary to raise 

 new questions and lead to further progress. In the complicated 

 domain of biology, and particularly in that of heredity, it is only 

 through theorising that new questions are raised, and the path to the 

 discovery of new facts pointed out. 



The assumption of the existence of biophors and determinants 

 seems to me as indispensable and quite as justifiable here as the 

 assumption of atoms and molecules in the domain of chemistry. 

 Modern philosophy would, indeed, be in the right in rejecting the idea 

 of philosophical atoms as minute indivisible particles ; the chemical 

 atom, on the other hand, is so far real, as it is the expression of the 

 relative weights in which the so-called elements combine together to 

 form molecules. Without the symbol of chemical atoms and molecules, 

 the whole marvellous deepening of chemical knowledge which the 

 century now drawing to its close has brought about would have been 

 impossible. In the same way, I believe that a deeper penetration into 

 the problems of biology, or at least into that of heredity, will only be 

 possible through the assumption of the symbols of biophors, of ids, 

 and above all of determinants ; and here also, when, with the help of 

 these symbols, we formulate our questions to Nature, we shall be 

 dealing, not with mere fanciful images, but with realities, just in the 

 same sense in which chemical atoms and molecules are realities. 



In my opinion, the belief that biology does not require the 

 guidance of theory is a great and widespread error. Within a very 

 limited range, an individual investigator may, without doubt, make 

 progress in certain directions without any conscious guiding theories — 

 that is, so to speak, with latent theories. In truth, however, if his 

 research be at all far-reaching, it is always guided by hypotheses, the 

 confirmation or refutation of which he seeks. But when an attempt is 

 made to investigate a wide domain embracing many phenomena, 

 unconscious assumptions are no longer sufficient ; but definite and 

 well -thought- out hypotheses belonging to a theoretical system are 

 necessary. This is what I have attempted to supply with my theory 

 of heredity, — not a structure calculated for eternity, but one which 

 should serve as a solid nucleus, a crystallisation-point, for further 

 research, and around which new acquisitions in knowledge should 

 group themselves for a time. I do not believe that any one now 

 living could think out and elaborate a theory of heredity which should 

 withstand the course of time without requiring modification. The 

 scientific general-staff is now so large, that no hypothesis can remain 

 long untested ; on the contrary, every new idea is at once seized hold 

 of by an army of investigators who seek, if possible, to refute it, or at 

 least to corroborate it. I do not understand how it can be seriously 

 urged at such a time, as an objection to a theory in the complicated 



