476 GROWTH OF BIOLOGY IN THE NINETEENTH CENTURY. 



essence as that from different albuniinous ])odies with special oroani- 

 zation will come a living cell. 



We therefore prefer, in the question which is occupying us, to leave 

 out both the concept of an atom and also the extraordinarily diificult 

 cx)ncept of a force of which so nuich misuse is made, and to i-onfine 

 ourselves to that by which alone a force can be known; that is to say, 

 to its effects. But in reference to these I think and may assert the 

 same thing as in reference to the organization of matter. 



Just as by the joining togethi'r of atoms to make molecules, of the 

 molccidrs to make the higher material units of th(» living cells, of liv- 

 ing cells to make })lants and animals, ever new, more numerous, and 

 higher forms of organizations are created, so it is with the effects 

 which proceed from them. With ever^^ one of the endless stages and 

 forms of oi'ganization new modes of action are produced; and when 

 the in\'estigator (-(jmes to plants and animals he has to do with an 

 entirely new world of unconmioiily manifold effects, which do not 

 occur in lifeless nature and which can not occur there, since the re(}ui- 

 site organization is wanting. I will instance only the preservation of 

 the species by growth and rej)roduction. metabolism, the different 

 kinds of irritability, phototaxis, ehemotaxis, geotropism, etc., con- 

 sciousiu^ss, faculties of sense and thought, and, linally, all the different 

 effects which single parts of cells exert upon each other, cell upon 

 cell, organ upon organ, animals and pliints uj)on one another. 



Is it the business of the physicist to concei'n himself with effects of 

 every kind which proceed from all the possible bodies in the world? 



Certainly not. As the chemist concerns himself oidy with the sim- 

 plest organization of matter, the chemical, but not with biological com- 

 l)inations, so the physicist, as a man of the science as it has historically 

 grown to be, concei'ns himself only with a certain class of effects, 

 w^hich may be called the elementary ones — a class of effects, in itself 

 considered, extraordinarily large, yet, in comparison with all the modes 

 of action in the world, very small. Should the physicist not choose to 

 impose this limitation upon himself, he would be obliged to unite in 

 one person the labor of the ph}' siologist and psychologist, the sociolo- 

 gist and historian, and whatever other study there may be. 



Finally, let it be remarked that the current opinion that the investi- 

 gation of life is nothing but a chemo-ph^'sical problem, and that 

 everything in the world is physics and chemistry, is commonh' con- 

 nected with a gross overvaluation of chemo-ph3'sical science. It seems 

 to be forgotten that this science, like everything human, is but a work 

 of detail (ein Stiickwerk), and at every point jostles against limits of 

 natural knowledge which, for the time being, seem to be insuperable, 

 and that chemistr}^ and physics in this regard have no advantage over 

 biology. 



Nageli well said, in 1877, in his address before the Munich congress 

 upon the "Limits of the knowledge of the natural sciences," that 



