THE ACTIVE FORCES OF LIVING ORGANISMS 39 



molecular environment of a given kind are alone 

 essential. These are also the chief factors in vegetal 

 growth ia which ethereal motion in the form of light 

 plays so important a part. 



Of all elements oxygen is admittedly the most The nega- 

 negative, or, in other words, the most attractive ; and oxygen. 

 although these terms are usually applied to it in an 

 electrical sense, yet all that we know of its behaviour 

 chemically justifies to a great extent an extension of 

 their meaning so as to cover this second form of 

 action. Electrical and chemical phenomena, espe- 

 cially in living matter, are so intimately connected 

 that it would probably be impossible to draw a clear 

 dividing line between them. When oxygen passes 

 from the capillary into the lymph surrounding the 

 tissues, it tends, we may suppose, by reason of its 

 attractive power, to group the other elements round 

 it so as to form new molecules, which, if the vibratory 

 conditions be favourable — that is to say, not excessive, 

 and yet sufficient — will then take place. In a similar 

 way, when the vibratory conditions become either too 

 weak or excessive, the oxygen breaks away from its 

 surroundings, forming new compounds. If the state 

 of oxidation of muscular tissue be variable, as we 

 have reason to suppose it is, this extreme negativity 

 of oxygen may be a factor of primary importance in 

 contraction ; for when the diffusive or attractive influ- 

 ence of oxygen is diminished, it would seem likely that 

 the elements in those bodies which remain should 

 possess a greater power of attraction for one another. 



