CHAPTER IV 



THE MOLECULAR CONSTITUTION OF LIVING MATTER AND ITS 

 INNATE TENDENCY TO VARIATION 



WHAT has hitherto been said goes to show that the properties 

 of all bodies alike are due to their molecular composition 

 and nature ; and that in the case of compound substances their 

 properties are wholly different from the properties of their con- 

 stituent elements, and cannot even be guessed at from a knowledge 

 of them. 



The capacity for undergoing changes in appearance and pro- 

 perties under the influence of changing external conditions has 

 been illustrated by a reference to some of the transformations that 

 occur in different kinds of matter when aggregated into the forms 

 of crystals and of lowest Uving units respectively. It was further- 

 more hinted that these changes and transformations could only 

 have been induced by reason of the new physical influences having 

 brought about some alteration in the molecular arrangement pre- 

 existing in the several substances ; and that, however easily such 

 changes are capable of being induced in crystalline matter, they 

 ought to be brought about still more easily in new-born living 

 matter, by reason of its far greater molecular complexity. 



We must look now a little more fully at this question of 

 molecular composition in order, if possible, to acquire some vague 

 notion as to the degree of its complicacy in living matter. 



It may surprise some to know that molecular corhposition is an 

 important item even with reference to substances that are looked 

 upon as elementary — different modes of composition or arrange- 

 ment of the atoms sufficing to produce in them what are called 

 ' allotropic ' states. We are most familiar with these as they are 

 presented to us in the various forms of carbon. The differences 

 between the diamond, graphite, anthracite, and pure charcoal are 

 most striking, and yet these are all different states of one and the 

 same substance whose ultimate atoms are differently grouped. 



Oxygen exists in two different states — ordinary oxygen, and 



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