THE BEGINNINGS OF LIFE. 1 1 7 



structures of simple organisms, like the forms and 

 molecular structures of crystals, are referrible to the 

 action of universal and immutable physical laws. 



All the evidence we have gathered together in this 

 and preceding chapters alike tends to show, that the 

 differences which exist between various kinds of matter 

 depend in the main upon differences in molecular 

 structure or mode of aggregation. This conclusion is 

 forced upon us by the phenomena of allotropism and 

 isomerism, by the consideration that thousands of 

 wholly different substances are compounded merely of 

 carbon, hydrogen, and oxygen in similar or different 

 proportions, and by multitudes of other facts of a like 

 nature. Some of these aggregates are stable, whilst 

 others are highly unstable. Slight external influences 

 suffice to alter the crystalline form of certain bodies, 

 some of which, such as mercuric iodide, undergo the 

 most remarkable changes. Such alterations are all 

 passages from one mode of statical aggregation to 

 another mode of statical aggregation. And yet crystal- 

 line matter is often capable of undergoing a very 

 different kind of rearrangement by which it is con- 

 verted into a colloid. The colloid is distinguished by 

 its extreme mutability its existence is a continual 

 metastasis. It is, in fact, a dynamical state of matter. 

 Further aggregations and rearrangements may take place 

 amongst its molecules and give rise to other forms of 

 matter possessing the mutability which distinguishes 



