THEORIES AND PROBLEMS OF CANCER 671 



are included in the body of the individual. Different groups of 

 cells are influenced by each other, the whole body being affected 

 by stimuli applied only to a part and what happens in the cells 

 of one part of the body may depend upon or may influence what 

 happens in the cells of other parts. The phenomena dependent 

 upon this correlation between the parts of the body of the 

 multicellular organism may all be included under the term 

 co-ordination. 



Some theories which profess to explain the nature of co- 

 ordination involve the acceptance of a metaphysical power 

 or influence; I refer particularly to Driesch's "Entelechy" — a 

 principle he postulates as controlling development, regeneration 

 and the interaction between the parts of living organisms. If 

 a sufficiency of physical facts be lacking to afford a satisfactory 

 explanation for a particular phenomenon, it may — or may not — 

 be reasonable to postulate some metaphysical agency to account 

 for it ; whether it be not safer to leave the phenomenon in part 

 unexplained in the hope of further evidence being discovered 

 is, to some extent, a matter of personal opinion ; if, however, an 

 explanation, which satisfies the requirements of the case, be 

 forthcoming which is based entirely upon observed facts, the 

 introduction of any metaphysical assumption would appear to 

 be quite unnecessary and undesirable from every point of view. 



In the explanation of the particular phenomena of co-ordina- 

 tion dealt with here, I think it will be found that no recourse to 

 powers or influences which are beyond proof or beyond our 

 understanding is in any way necessary. 



Among the higher animals what is perhaps most generally 

 understood by co-ordination is a consequence of the existence 

 of a nervous system. Returning to the example of a man whose 

 toe is trodden upon, the reaction takes place because the 

 stimulus applied to the toe is conveyed to the brain through 

 the nerves ; the brain in response sends impulses through 

 other nerves both to the stimulated part and to other parts 

 of the body, producing a number of movements which include 

 many more parts of the body than that to which the stimulus 

 was applied. These responses to stimuli are dependent upon 

 the continuity of the nervous system : if the nerves of any 

 part of the body in man or one of the higher animals be 

 separated from the brain, the usual sequence of events following 

 a stimulus is interrupted — the movements, in fact, are said to 



