186 THE STUDY OF ANIMAL LIFE CHAP. 



It seems to many that no chemico-physical description 

 has yet been given of a single vital operation, such as 

 the contraction of a muscle, and that we cannot satis- 

 factorily describe in mechanical terms either the linkage 

 of events in a particular function, or the harmonising of 

 one set of internal activities with another, or the co- 

 ordination of acts in a piece of behaviour. 



As to individual development, we cannot give a 

 mechanical description of such facts as the condensation 

 of the inheritance into a germ-cell, or of the differentia- 

 tion of the embryo, or of the remarkable regulation- 

 phenomena that are exhibited when an embryo rights 

 itself after the building materials of its living edifice have 

 been seriously disarranged, or of the way in which many 

 developing parts seem to work into each other's hands, 

 as if conspiring towards some distant result. 



Similarly, as regards organic evolution, we cannot 

 offer a mechanical theory of variability. Even the pro- 

 cess of selection or sifting that goes on in Nature is more 

 than mechanical. The evolving organism is an historical 

 being, trading with time ; and the humblest creatures 

 are in their mutations creative. Without asking the 

 student to accept these statements which are rather 

 assertions than arguments we advise him to suspend 

 judgment and not to be in a hurry in concluding that 

 mechanical formula suffice for answering the distinc- 

 tively biological questions. 



5. The Uniqueness of Life. When all is said there is 

 no getting away from the big fact that living creatures are 

 very different from things in general. They are also very 

 different from machines, in regard to which it should be 

 remembered that they are not fair samples of the inorganic 

 world, having, so to speak, a human idea inside them. 



(a) To some investigators it seems enough to say that 

 living creatures differ from crystals and stones in their 

 much greater complexity of architecture and of internal 

 change. Their visible and invisible configurations and 

 collocations are so intricate that they must be studied 

 apart. But they do not require new formulae or con- 

 cepts for their description, 



