394 RESPIRATION 



us to define more and more accurately and fully. Only when an 

 organism is dead do we seem to have before us a physical and 

 chemical complex. 



Those who insist that physiological activity must in reality be 

 physical and chemical change have to answer a previous ques- 

 tion as to the justification for the assumption of physical and 

 chemical reality. The molecules, atoms, and electrons of the 

 physical sciences seem real enough so long as we confine ourselves 

 to the superficial aspect of reality which is dealt with by the 

 physical sciences; but it is the same reality that is dealt with by 

 biology, and we reach a different interpretation of it through the 

 study of biological phenomena. In this interpretation the self- 

 existent individuality of atoms and molecules fades away in rela- 

 tivity. 



The modern world has become so accustomed to the material- 

 istic assumption which identifies the mechanical interpretation of 

 reality with actual reality that in spite of the existence of biology, 

 psychology, ethics, religion, and philosophy it is difficult at pres- 

 ent to obtain even a hearing for the view that physical reality rep- 

 resents no more than superficial sensuous appearance. By the help 

 of various makeshift hypotheses such as those of vitalism or 

 animism, the real philosophical problem as to the ultimate validity 

 of the physical interpretation of reality has been evaded for the 

 time. But these evasions cannot satisfy us, and the problem comes 

 up in a clear-cut and definite form in connection with the relation 

 of biology to physics and chemistry. The facts dealt with in the 

 latter sciences present us with one interpretation of "reality," or 

 "nature," and those dealt with by the former present us with a 

 different one. 



Which of the two interpretations corresponds more closely to 

 actual reality? There appears to me to be no doubt that the biolog- 

 ical interpretation does. The progress of the physical sciences 

 has taught us that the gases, liquids, and solids which to super- 

 ficial examination appeared to be continuous and inert substances 

 are not only discrete but made up of molecules in continuous 

 relative movement, and, in the case at least of solids and liquids, 

 continuously affecting one another's movements and properties. 

 We now know also that atoms themselves are systems of still more 

 elementary units moving relatively to one another at enormous 

 velocities, and that in chemical combination, and even in solution 

 or what we call simple mechanical interaction, these systems are 

 modified, as shown, by electrical phenomena. The chemist can 



