THE CHARACTERISTICS OF ORGANISMS 31 



movement so that various parts of it get a chance of meeting the 

 nucleus, which, so to speak, tempts them to settle down — freezii g 

 into architecture. Into the physics of this we need not here enter; 

 our point is simply that in a suitable environment, with time and 

 quiet, a crystal-unit "grows". By accretion it becomes a handsome 

 large crystal. On to its faces other crystal-units are added, and on 

 the new faces more again, until there is formed- an edifice. A 

 distinction must be made between the molecule, say of silicon- 

 dioxide (SiOa), and the crystal-unit of quartz, which consists of 

 three molecules of silicon-dioxide, arranged in some screw-like way; 

 so here already we see conditions of variability. 



The crystal increases in size in an orderly way; how does this 

 differ from the growth of an animal or a plant? Is there a real 

 resemblance, or is it a misleading analogy? The first answer is that 

 a crystal increases in size at the expense of material, usually a 

 solution, that is chemically the same as itself; whereas animals 

 and plants feed on substances different from their own living 

 matter — often very different. This is sound commonsense, and yet 

 the edge is taken off it a little by two facts, first that it is possible 

 to feed an amoeba on amoebae, or a tadpole on tadpoles, or a rat 

 on rats; and, secondly, it is possible to increase the size of a crystal 

 when it is placed in a solution of a chemically different substance, 

 which has, however, the same form of crystallisation. 



Then one might lay emphasis on the fact that the increase in 

 the size and weight of a crystal is by accretion from without, 

 whereas organisms grow by taking in raw materials, altering these, 

 and building from within. In the growth of seeds and eggs and 

 the like, there is obviously a utilisation of a previously accumulated 

 store of condensed food. We see then that the crystal grows from 

 without, by the addition of new crystal-units on the faces of those 

 already existing, whereas organisms grow from within. 



But there is another, more general, way of looking at the differ- 

 ence between crystal increase and organic growth: the one is 

 passive and the other is active. It is not so much that the crystal 

 grows, as that it is added to by other crystal units — usually, more- 

 over, in saturated solution. But an organism actively takes in its 

 food, actively changes and distributes it, and actively builds with it. 



But some authorities who press the analogy between crystals 

 and creatures bring forward another supposed resemblance. If a 

 crystal is broken there is a neat mending, provided there is the 

 proper environment. There is more rapid accretion at the broken 

 surface than elsewhere; the repair is often in proportion. This is 

 very suggestive of the way in which an animal or a plant replaces 

 a lost part or repairs an injury. If a crystal be broken into two, 

 each half may form a perfect whole. If a Planarian worm or a 

 Hydra be cut across, each half usually "regenerates" an entire 



