330 The Unity of the Organism 



while the iron piece is black. 



See now what this means. Actually, as is well known to 

 every beginning student in analytical chemistry, these two 

 metals are very similar in color as well as in other physical 

 attributes — so much so, in fact, that some authors apply 

 the same term "silver white" to both. What a housekeeper 

 really means when she says she knows one implement to be 

 of nickel because it is bright and the other to be of iron 

 because it is black, is that she is depending on a chemical 

 rather than a physical attribute for a distinguishing mark ; 

 the attribute, that is, in virtue of which iron is acted upon 

 much more readily by oxygen in the presence of moisture 

 than is nickel. The much greater liability of iron than 

 nickel to tarnish and rust is a chemical rather than a phy- 

 sical difference between them. This fact, namely that of 

 the dependence of distinguishing differences between sub- 

 stances more upon chemical than upon physical attributes is 

 of very wide applicability in nature, and is greatly impor- 

 tant both scientifically and philosophically. 



Now turn from comparing these two elementary chemical 

 substances to a comparison of any two human organisms, or 

 persons who might be members of a household to Avhich 

 the implements might belong. And make the comparison first 

 on the basis of the ph3^sical attributes just as we began 

 comparing the implements of nickel and iron. Does any 

 reader doubt that he would find it much easier to distinguish 

 the persons than the metals.'^ As to purely morphological, 

 that is, physical differences between almost any two persons 

 (with the possible exception of certain rare instances of 

 "identical" twins), there is no room for question. General 

 shape of head, face and features, and the size and propor- 

 tions of the various parts of the body furnish many unmis- 

 takable distinguishing attributes. 



