114 THE DATA OF BIOLOGY. 



• 

 reply that under cover of this inability to make a specifica- 

 tion of terms that shall be adequately comprehensive, there 

 is concealed the inability to conceive the required terms in 

 any way. 



Thus a critical testing of the definition brings us, in an- 

 other way, to the conclusion reached above, that that which 

 gives the substance to our idea of Life is a certain unspecified 

 principle of activity. The dynamic element in life is its 

 essential element. 



§ 36c. Under what form are we to conceive this d3rriamic 

 element? Is this principle of activity inherent in organic 

 matter, or is it something superadded? Of these alternative 

 suppositions let us begin with the last. 



As I have remarked, in another place, the worth of an 

 hypothesis may be judged from its genealogy ; and so judged 

 the hypothesis of an independent vital principal does not 

 commend itself. Its history carries us back to the ghost- 

 theory of the savage. Suggested by experiences of dreams, 

 there arises belief in a double — a second self which wanders 

 away during sleep and has adventures but comes back on 

 waking ; which deserts the body during abnormal insensibility 

 of one or other kind; and which is absent for a long period 

 at death, though even then is expected eventually to return. 

 This indwelling other-self, which can leave the body at will, 

 is by-and-by regarded as able to enter the bodies of fellow 

 men or of animals ; or again, by implication, as liable to have 

 its place usurped by the intruding doubles of fellow men, 

 living or dead, which cause fits or other ills. Along with 

 these developments its quality changes. At first thought of 

 as quite material it is gradually de-materialized, and in ad- 

 vanced times comes to be regarded as spirit or breath; as 

 we see in ancient religious books, where " giving up the 

 ghost " is shown by the emergence of a small floating figure 

 from the mouth of a dying man. This indwelling second 

 self, more and more conceived as the real self which uses the 



