306 C. M. CHILD 



ism for this reaction does not exist wholly in the acid, nor does 

 itexist wholly in the cells at the anterior end of the above piece 

 it exists in the acid plus the metal and in these cells plus other 

 cells. Driesch's attempt to reduce the 'machine theory' to 

 absurdity by the argument that since any part of a harmonious 

 equipotential system is capable of producing any other part, 

 therefore, according to the machine theory, each part must repre- 

 sent at all times all possible parts of an infinite number of machines, 

 which is manifestly absurd, is itself absurd because no such 

 assumption is necessary. A given part represents one machine, 

 or a component of such a machine, at a given time; at another 

 time if its relations to other parts have changed, it may repre- 

 sent another machine or component. To maintain that such a 

 part possesses the same potences under these different conditions 

 means simply that its constitution is capable under the proper 

 conditions of changes which make possible a certain different 

 series of reactions: it certainly does not mean that it possesses 

 the same constitution at all times. At any given time the consti- 

 tution of parts which are equipotential in this sense may differ 

 widely. 



But I believe it is misleading to designate such parts as equipo- 

 tential. As parts of a system at any given time they are not 

 equipotential, for they possess different constitutions as the facts 

 show, in short the piece of Planaria which is capable of regula- 

 tion is never an equipotential system. The more closely it 

 approaches to equipotentiality, the less capable of regulation, or 

 indeed of life it becomes. The apparent eauipotentiality in 

 some eggs and m some of the lower organisms is undoubtedly 

 merely apparent, in so far as these forms are capable of d'^velop- 

 ment or regulation. As in the case of Planaria, it will disappear 

 as soon as isolation of parts and analysis of results is extended 

 sufficiently far. I think we may say that there is at present no 

 valid evidence for the belief that any living system which is 

 undergoing regulation or development in nature is at any given 

 time an equipotential system. We cannot properly speak of 

 the potentialities of parts unless we assume that their constitu- 

 tion remains constant : a change in constitution means a new part 



