INTRODUCTION 9 



deeply the physiologist endeavours to peer into the processes within 

 the living cells, has led some, even at the present day, to the assump- 

 tion of some special quality in living organisms which is designated as 

 ' vital force ' or ' vital activity.' Such views are classified together 

 under the term vitalism. From his beginning man has been accustomed 

 to draw a sharp line of distinction between those phenomena which 

 by their constant occurrence seemed to him natural, and therefore 

 explicable, and those phenomena of which he could not see the deter- 

 mining antecedent, and which were to him, therefore, anemic and 

 capricious. To the latter he set up graven images, and not perceiving 

 his own springs of action, endowed them with a self-determining 

 personality such as he imagined himself to possess. This procedure, 

 though possessing certain advantages in allowing him to perform his 

 common duties free from the ever-lurking fear of supernatural inter- 

 ference, suffered from the great drawback that it fenced off unknown 

 phenomena as unknowable and not to be known. It has therefore 

 acted as a continual check on the growth of man's knowledge and 

 control of his environment. Such a graven image is vitalism. As a 

 working hypothesis it must be sterile. Just as the hypothesis of special 

 creation would impede all research into the relationships of animals 

 and plants, so vitalism would stay the hand of the physiologist in his 

 endeavours to determine the changes which occur within the living 

 organism. In many cases, however, the terms ' vitalism ' and its 

 antithesis ' mechanism ' are used unjustifiably. The production of 

 energy within the body is due to the oxidation of the food-stuffs. In 

 certain functions it is not yet fully established whether the changes 

 involved take place at the expense of the energy, hydrostatic pressure 

 or otherwise, of the fluids outside the cells, or whether energy is 

 supplied to the process by the cells themselves at the expense of 

 oxidative changes occurring in their living substance. Both views are 

 possible, but the adoption of either by a physiologist does not justify 

 the statement that he is a ' vitalist,' ' neo-vitalist,' or ' mechanist.' 

 The office of the physiologist is the determination of the changes which 

 occur in the living body and the establishment of the causal nexus 

 (i.e. the routine of sequences) between them. For such a man to 

 describe himself as a vitalist or mechanist is as germane to the subject 

 as if he were to call himself a Trinitarian or a Plymouth Brother. 



Throughout this chapter we have assumed no necessary dividing 

 line between the different classes of phenomena in the conceptual 

 universe, although in the present state of our knowledge we are far 

 from being able to include the whole of them under the same general 

 laws. It might be objected that in taking up this attitude we had 

 left out of account one supreme fact, viz. the existence of conscious- 

 ness in ourselves. As a comparative and objective study, however, 



