HEREDITY FROM PHYSICO-CHEMICAL POINT OF VIEW. 69 



It is possible to say that each yeast cell inherits its properties 

 from the mother cell; but such a phrase serves merely to indicate 

 that the character of the transformation depends upon the char- 

 acter of the germ or proliferating organism itself, rather than 

 upon the character of the material which is transformed under 

 its influence. A mould or bacterium in the same medium effects 

 a totally different kind of transformation, but one equally specific 

 and equally true to the character of the introduced germ. 



In general the possession of this automatic property of specific 

 structural and chemical synthesis constitutes the most funda- 

 mental distinction between the living and the non-living material 

 systems found in nature. We observe that all organisms and all 

 living cells without exception possess this power; they transform 

 certain inert materials selected from the surroundings into their 

 own characteristically organized and physiologically active living 

 substance. The materials thus incorporated and transformed 

 differ widely in their character and accessibility in different 

 organisms ; at the one extreme are green plants living on carbon 

 dioxide, salts, and water; at the other extreme is man in his com- 

 plex social environment. But this difference of degree does not 

 alter the fundamental identity of kind. Wherever we find life 

 we find exhibited this unique property of specific construction 

 or synthesis, whether the product of the construction is simple 

 or complex. 



This property also manifests itself in another and less evident 

 manner. The specific organization of any animal or plant, with 

 the associated physiological activity, not only originates in this 

 manner as the product of growth from the parent organism, but 

 once reached, it has to be maintained. And this maintenance in- 

 volves the activity of specific construction in just as full a sense 

 as does growth or development from the germ. During life the 

 organized living substance is continually being destroyed, and 

 must as continually be replaced. This becomes especially evi- 

 dent in certain of the lower animals whenever the food-supply is 

 withdrawn; the quantity of living substance then undergoes 

 progressive reduction, which may proceed until only a small 

 fraction of its original quantity is left; a planarian may thus be 

 reduced by starvation to a quarter of its original length without 



