I] OF LIFE ITSELF 15 



legitimate postulate of the physicist, in approaching the physical 

 problems of the living body, is that with these physical phenomena 

 no ahen influence interferes. But the postulate, though it is certainly 

 legitimate, and though it is the proper and necessary prelude to 

 scientific enquiry, may some day be proven to be untrue; and its 

 disproof will not be to the physicist's confusion, but will come as 

 his reward. In dealing with forms which are so concomitant with 

 life that they are seemingly controlled by life, it is in no spirit of 

 arrogant assertiveness if the physicist begins his argument, after the 

 fashion of a most illustrious exemplar, with the old formula of 

 scholastic challenge: An Vita sit? Dico quod non. 



The terms Growth and Form, which make up the title of this book, 

 are to be understood, as I need hardly say, in their relation to the 

 study of organisms. We want to see how, in some cases at least, 

 the forms of living things, and of the parts of living things, can be 

 explained by physical considerations, and to realise that in general 

 no organic forms exist save such as are in conformity with physical 

 and mathematical laws. And while growth is a somewhat vague 

 word for a very complex matter, which may depend on various 

 things, from simple imbibition of water to the complicated results 

 of the chemistry of nutrition, it deserves to be studied in relation 

 to form : whether it proceed by simple increase of size without obvious 

 alteration of form, or whether it so proceed as to bring about a 

 gradual change of form and the slow development of a more or less 

 complicated structure. 



In the Newtonian language* of elementary physics, force is 

 recognised by its action in producing or in changing motion, or 

 in preventing change of motion or in maintaining rest. When we 

 deal with matter in the concrete, force does not, strictly speaking, 

 enter into the question, for force, unlike matter, has no independent 

 objective existence. It is energy in its various forms, known or 

 unknown, that acts upon matter. But when we abstract our 

 thoughts from the material to its form, or from the thing moved to 

 its motions, when we deal with the subjective conceptions of form, 



* It is neither unnecessary nor superfluous to explain that physics is passing 

 through an empirical phase into a phase of pure mathematical reasoning. But 

 when we use physics to interpret and elucidate our biology, it is the old-fashioned 

 empirical physics which we endeavour, and are alone able, to apply. 



