Il6 THE CAUSATION OF DISEASE. 



an actuality; for it is, as we have seen, in large measure, an 

 inverted evolution, and when a structure is taken to pieces in 

 the inverse order to that in which it was put together, there 

 are necessarily revealed characters which belonged to the indi- 

 vidual at successive periods of his evolution. Characters 

 which were before potential now become actual. This method 

 of potential manifestation may be illustrated very simply. 

 At a certain stage in the building, or evolution, of a house, 

 before the roof has been put on or the windows fixed, it will 

 be both draughty and, in rainy weather, wet ; but when the 

 house is finished — when its evolution is complete — it will,, 

 if properly constructed, become perfectly dry and free from 

 draughts. If, now, we invert the evolution, and cause a partial 

 dissolution by removing the roof and taking out the windows,, 

 the house will again display characters which belonged to it 

 at a certain stage of its evolutionary career: it will become 

 once more damp and draughty. Characters, before potential 

 only, now become actual. 



Yet another example may be given. The process of evolu- 

 tion may be observed in the invention and gradual improvement,, 

 during the long course of years, of a machine, until, finally, 

 perfection is reached — that is to say, the highest possible pitch 

 of adequacy. Owing to the enormous competition between 

 different machines, belonging, as we may say, to the same 

 species, there is a struggle among them for existence, and this, 

 struggle will eventuate in the survival of the fittest. Every 

 new improvement is, as it were, a happy variation, which will 

 be seized upon by the market, which constitutes, so to speak,, 

 the environment ; and thus, by an accumulation of improve- 

 ments (natural variations), perfection is at length attained. It 

 is true that, as the evolution proceeds, there is not necessarily 

 an increased aggregation of matter, nor a greater complexity of 

 structure, for sometimes a great improvement may be made 

 by simplifying the structure and diminishing the bulk, and in 

 such cases the various phases in evolution would not fulfil the 

 terms of Spencer's formula. But this is simply because that 

 artificial evolution which is the product of man's mind, is less 

 orderly and perfect in its progress than the unconscious evolu- 

 tion which isever at work throughout Nature. It not unfrequently: 



