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him that this substance is composed of an immense number of mutual- 

 ly identical units, all of which are in active motion; furthermore, that 

 each of these molecules is again composed of 45 smaller units, com- 

 prising three different kinds, the so-called atoms, that are also subject 

 to various movements inside the molecular combination. And if one 

 considers each one of these atoms, the physicist will tell you that these 

 represent a small body, referred to as the nucleus, surrounded at 

 relatively great distances by infinitcsimally small particles moving 

 around the nucleus at enormous speed. And even the nucleus is far 

 from homogeneous; various components, in part still incompletely 

 characterized, appear to exist therein, and to carry out all sorts of 

 curious motions. 



This, then, is the physicist's fairy tale; nevertheless, the atomic bomb 

 is an eloquent testimony to the significance of this picture. But I 

 might, and with equal justification, have regaled you with one of the 

 many fairy tales of the geologist, or with the most beautiful fairy tale 

 of all, the astronomer's concept of the structure of the universe. Time 

 does not permit this ; it is, however, certain that the capacity of the 

 layman to imagine these things is scarcely adequate. 



Now I realize full well that many of my colleagues will be severely 

 shocked when they find their most profound concepts designated as 

 fairy tales. In this context I should like to remark that these concepts 

 have not developed overnight; many others have preceded the current 

 version, and it is far from certain that the latter will not be succeeded 

 by still different ones. It is therefore possible to speak only of various 

 degrees of certainty as approximations to reality. Hence I want to 

 express the hope that you will also grant the microbiologist his fairy 

 tale; for such tales derive their value from their nature as working 

 hypotheses, and as such they inspire the investigations that eventu- 

 ally will increase man's comprehension of nature. 



Meanwhile, it is high time to return to my point of departure, and 

 to attempt a summary of the microbiologist's concept of life. He does 

 not recognize merely the virtual ubiquity of life, but also the abun- 

 dant significance of the invisible part of life that exists, as it were, 

 underground; furthermore, the complete mutual dependence of both 

 the higher and the lower forms of life; and, above all, the surprising 

 diversity in the manner in which different living beings have succeeded 



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