392 RESPIRATION 



and organic activity only the activity which expresses itself in 

 organic structure, the two branches of biology are in reality one, 

 and we may look forward to a time when the present wholly 

 artificial and sterilizing separation of them will disappear along 

 with the disappearance of the mechanistic theory to which the 

 separation is due. 



The true scientific procedure of biology is different from that 

 of the physical sciences. In physics and chemistry the procedure 

 employed is to ascertain the properties of the separate units of 

 matter and energy with which it is assumed that these sciences 

 deal. Thus from the properties and movements of the parts of a 

 material system such as a machine we can predict its behavior 

 and can design and control machinery. From the properties and 

 movements of the molecules in a given quantity of gas we can 

 predict its behavior. From the properties of the atoms of carbon 

 and other elements we can predict the existence and many of the 

 properties of carbonaceous and other compounds. But we cannot 

 predict in this way the behavior of a living organism. The re- 

 lationships, for instance, into which the carbon atoms as inter- 

 preted by chemistry enter within living organisms show them- 

 selves to be too complex and changeable, so that, apart from the 

 biological method of treatment, we should be totally at a loss. In 

 the physical sciences we are looking at collections of units, each of 

 which is looked at from the outside. In biology we are looking at 

 each unit from the inside, and biological results afford abundant 

 justification for this method of looking at them. 



It may appear at first sight as if the biological method were 

 unscientific, and the claim may be made that it ought to be, and 

 ultimately must be, possible to advance in biology by the method 

 of the physical sciences. This claim must now be examined care- 

 fully. 



The reason why the physical or chemical method of treatment 

 is so unsatisfactory in biology is that in connection with living 

 organisms the properties of the parts show peculiarities which we 

 do not meet with in what we distinguish as the inorganic world. 

 Let us take the case of nitrogen atoms. When nitrogen is pres- 

 ent as a gas at an ordinary temperature the properties of its mole- 

 cules seem to be very simple for all practical purposes. The mole- 

 cules simply repel one another when they meet, or when they 

 encounter molecules of other gases; and the kinetic theory of 

 gases, based on this simple assumption, enables us to predict with 

 the greatest accuracy the behavior at ordinary temperatures and 



