36 MIND IN EVOLUTION , CHAP. 



tions of the part affected. Now this is what mutilations, 

 particularly those of the embryo, disprove. If the 

 embryo is a machine for the assimilation, storage, and 

 modification of material or of energy whereby the mature 

 organism is to be produced, then there is no doubt that in 

 its normal life-history one portion of this machine resides 

 in one blastomere and another in another. But experi- 

 ment shows that one blastomere artifically separated can 

 generate the entire organism, and the advocates of the 

 mechanical view are thrown back on the suggestion that 

 nature has provided a secondary set of these highly perfect 

 machines in case of accidents accidents, moreover, which 

 are by no means likely to occur except in the laboratory, 

 an environment which nature can hardly have foreseen. 

 Machines, as Driesch has elaborately argued, can do 

 wonderful things, but what do we ordinarily expect 

 of a broken machine ? 



On the other hand, the teleological view is full of diffi- 

 culty. We do not by taking thought heal our wounds. 

 Our purposive activity supplies unguents and bandages, 

 but " the rest nature transacts within." Our tissue is 

 not, as far as we know, consciously aware of the purpose 

 of restoring itself. Nor can we suppose the stem of 

 Tubularia to plan the production of a new head. What 

 we do know is that an organism subject to injury or 

 distress not sufficient to overwhelm it, is stimulated to 

 intense effort. If it does not know how to act it never- 

 theless acts, and continually varies its action, abandoning 

 that which is fruitless and persisting in that which yields 

 relief. We shall see in the following chapters how by 

 this method living beings frequently obtain satisfactory 

 results which apparently they could not plan or foresee. 

 To conceive restorative vital processes to depend on 

 conation in this rudimentary form, we must suppose 

 successive stages in the process, each of which is satis- 

 factory by comparison with the preceding, but gives rise 

 to renewed efforts. We must also suppose the effort to 

 be made by each part of the organism affected, and must 

 assume a possibility of co-operation. This is to postulate 

 an arrangement certainly, but not an arrangement that is 



