4 THE PHYSICAL BASIS OF LIFE 



substances, advisedly; for it is here in the first place, that 

 Huxley's statements now require recasting in more mod- 

 ern terms. To many readers his discussion conveyed the 

 impression that protoplasm is a single chemical substance 

 or "living protein." In his opening words he spoke of 

 the physical basis of life as "some one kind of matter 

 common to all living beings. ' ' He pictured a union of life- 

 less substances, such as water, anmionia and carbon diox- 

 ide, to form "the still more complex body, protoplasm"; 

 and the properties of this substance, he affirmed, must re- 

 sult from the nature and disposition of its molecules. 

 ' ' The thoughts to which I am now giving utterance, ' ' said 

 Huxley, "and your thoughts regarding them, are the ex- 

 pression of molecular changes in that matter of life which 

 is the source of our other vital phenomena." 



In a broad sense these words are true; but evidently 

 they do not express the whole truth. Long ago it became 

 perfectly clear that what we call protoplasm is not chemi- 

 cally a single, homogeneous substance. It is a mixture of 

 many substances, a mixture in high degree complex and 

 the seat of varied and incessant chemical transforma- 

 tions, yet one which somehow holds fast for countless gen- 

 erations to its own specific type. How, in view of all this, 

 can we speak of a molecule of protoplasm ^. We might in- 

 deed suppose — it actually has been supposed — that pro- 

 toplasm consists of very large molecules (plastidules, mi- 

 cellae or biogens) into which all these various substances, 

 or their components, may be built ; but even were such an 

 hypothesis tenable it would leave out of account precisely 

 that which to many investigators seems the most funda- 

 mental part of the problem. The evidence from every 

 source demonstrates that the cell is a complex organism, 

 a microcosm, a living system. With the microscope we 

 distinguish in this system (Fig. l)"* a clear and appar- 



