X.] ORGANIZATION. ' 115 



The most obvious answer to this question perhaps would 

 be, that the structure of a crystal is alike throughout and 

 in every part, but that of an organism is different in dif- 

 ferent parts ; the leaves and the wood of a tree, for instance, 

 are of different structure, and so are the bones, the 

 muscles, and the nerves of an animal. But we have seen 

 that though crystals are generally perfectly alike in struc- 

 ture throughout, there are some perfectly regular crystals, 

 which, when they are examined by the infallible test of 

 polarised light, show a difference of structure between 

 their different parts. 



The essential difference between organization and any 

 kind of inorganic structure is quite different from this : 

 organization is the adaptation of structure to function. Organiza- 

 This principle, of adaptation of structure to function, and g°^j_ ^" 

 of one structure and one function of an organism to 

 another, is characteristic of the organic creation, and is 

 utterly unlike anything that we meet with in the 

 inorganic world. 



There are three principles of logical relation, that run Three re- 

 like guiding threads through physical science. These are — scieMe T 



1. The relation of cause and effect ; Cause, 



2. Tlie relation of resemblance and difference ; and Resem- 



. blance, 



3. The relation of means and purpose. Purpose. 



For the sake of brevity let us call these cause, resem- 

 blance, and purpose. Of course I do not offer this as a 

 complete enumeration of all possible relations : I well 

 know that it is nothing of the kind, I only say that, as a 

 matter of fact, these are the most important relations that 



we meet with in the physical sciences. 



The relation of cause is almost the only one that the Sciences 

 dynamical sciences have to do with : under which title I 

 include not only general dynamics, but the sciences of 

 sound, radiance, heat, electricity, and magnetism ; which 

 are all now recognised as special cases of dynamical theory. 

 And the same is, in a great degree, true of those more Chemistry, 

 elementary branches of chemistry that have to do with 

 the general properties of matter, and with the relations of 

 composition and decomposition to heat and to electricity. 



i2 



