RESPIRATION 395 



determine with great apparent accuracy the proportions of hydro- 

 chloric acid and water in an aqueous solution. In actual fact there 

 may be practically no hydrochloric acid molecules present and far 

 fewer simple molecules of water than would appear from the 

 analysis, since the molecules are partly ionized and partly com- 

 bined with one another in various forms. Consequently the re- 

 sults of the analysis represent only a ''practical" convention, how- 

 ever useful this convention may be. In reality the properties 

 of both the conventional hydrochloric acid and the conven- 

 tional water depend on the particular conditions existing in the 

 solution. But the inquiry can be, and has been, pushed still further. 

 At first sight it seems as if, in whatever way the molecules of 

 water and hydrochloric acid may be split up or combined, the 

 mass present is something independent of changeable relations. 

 But here, again, the progress of physical science has indicated 

 that even the mass of what is present depends upon relative move- 

 ment, and finally that absolute movement in empty space is a 

 conception to which no experimentally verifiable meaning can be 

 attached. 



We only deceive ourselves when we imagine that in physical 

 and chemical investigation we are free of relativity. Behind 

 all the superficial appearances of a ''real" physical world, rela- 

 tivity finally appears ; but in biological phenomena the relativity 

 is always evident and prominent, and precludes the possibility of 

 even a conventional physical and chemical interpretation of 

 the observed facts. In frankly accepting relativity, and framing 

 her interpretations on a principle based upon it, biology comes a 

 step nearer to actual reality than the physical sciences. 



It has come to be popularly believed that if we knew enough 

 of the physics and chemistry of what occurs in a living organism 

 biological interpretation could be reduced to physical and chemi- 

 cal interpretation. Though the attempts to give physical and 

 chemical interpretations of biological phenomena have never been 

 successful, and their failure in detail is becoming more and more 

 evident with the progress of both physiological and physical in- 

 vestigation, labored endeavors are still made to teach physiology 

 and represent the growing body of physiological knowledge in 

 physical and chemical terms. The investigations described in the 

 present book illustrate the fruitlessness of these attempts. In the 

 phenomena connected with breathing we are everywhere dealing 

 with organic regulation — in other words with the manifestations 

 amid superficial changes which at first sight puzzle and confuse 



