8 THE PHYSICAL BASIS OF LIFE 



the cell. ' " It is tins view of the physical basis of life that 

 has impressed us more and more as our knowledge of the 

 cell has advanced ; and this is as true of the physiologist 

 and the chemist as of the cytologist. I quote a distin- 

 guished biochemist. "We can not," says Professor Hop- 

 kins, ''without gross misuse of terms, speak of the 

 cell-life as being associated with any particular type of 

 molecule. Its life is the expression of a particular dy- 

 namic equilibrium which obtains in a polyphasic system. 

 Certain of the phases may be separated, but life is a prop- 

 erty of the cell as a whole, because it depends upon the 

 equilibrium displayed by the totality of co-existing 

 phases. ' '" This conclusion is precisely the same as that of 

 the cytologist ; for him, as has often been said, the word 

 protoplasm stands for a morphological concept, not for a 

 chemical one. 



At present we know living systems only in the form of 

 cells or their products ; for every organism is, or at some 

 time has been, a cell. I repeat, therefore, that when we 

 speak of protoplasm as the physical basis of life, we mean 

 simply the sum total of all the substances that play any 

 active part in the cell-life ; and certainly we can not limit 

 the list to such substances as the proteins, carl^ohydrates 

 or lipins. We must include a multitude of others, not ex- 

 cepting inorganic salts and water, which are often char- 

 acterized as "lifeless." At first sight this may seem a 

 rather barren conclusion ; but the fact is quite otherwise. 

 No conception of modern biology offers greater promise 

 for the physico-chemical analysis of vital phenomena 

 than that the cell is a colloidal system ; and that what we 

 call life is, in the words of Czapek, a complex of innumer- 

 able chemical reactions in the substance of this system. 

 Modern investigation has indeed already profited so 

 much by the point of view here offered as to suggest that 



