xvni THE ELEMENTS AND LIFE 357 



proportions. We can imagine, therefore, what endless 

 diversities arise when to these are added any of nine other 

 elements, and these in varying proportions, as well as being 

 grouped in every possible manner. 



The fact of " isomerism," or of different substances, often 

 with very different properties, having the very same chemical 

 composition, is now so familiar to chemists as to excite 

 comparatively little attention, yet it is really a marvel and a 

 mystery almost equal to that of the organic cell itself. It is 

 probably dependent upon the highly complex nature of the 

 molecules of the elements, and also of the atoms of which 

 these molecules are built up ; while atoms themselves are 

 now believed to be complex systems of electrons, which are 

 held to be the units of electricity and of matter. It is these 

 electrons and their mysterious forces that give to matter all 

 its mechanical, physical, and chemical properties, including 

 those which, in the highly complex protoplasm, have rendered 

 possible that whole world of life we have been considering in 

 the present volume. 



Here, then, we find, as before, that the farther back we go 

 towards the innermost nature of matter, of life, or of mind, 

 we meet with new complications, new forces, new agencies, 

 all pointing in one direction towards the final outcome — 

 the building up of a living sentient form, which should be 

 the means of development of the enduring spirit of man. 



Important and Unimportant Elements 



If we look at the long list of between seventy and eighty 

 elements now known we shall see that a comparatively small 

 number of these (less than one-fourth) seem to play any 

 important part either in the structure of the earth as a planet, 

 or in the constitution of the organised beings that have been 

 developed upon it. The most important of the elements is 

 oxygen, which is not only an essential in the structure of all 

 living things, but forms a large part of the air and the water 

 which are essential to their continued existence. It is also 

 a constituent of almost every mineral and rock, and is 

 estimated to form about 47 per cent of the whole mass of 

 the globe. The next most abundant elements are silicon, 

 aluminium, and iron, which form 25, 8, and 7 per cent 



