CRUSTACEA AND MOLLUSCS 23 1 



their constituents by a method that we call "analysis." 

 But this analysis can only continue until we reach the 

 elements. It is the characteristic of these that, however 

 much you subdivide them, the particles are always of 

 the same kind. They consist of a single form of matter. 

 Take gold, for instance ; however small it is ground up 

 or chemically divided, it remains gold. 



We have now analysed all the substances on the 

 earth, including the substance of which living things are 

 composed. It has been found that the living substance 

 contains just the same elements that we find in the 

 lifeless crust of the earth, in the inorganic world, as we 

 say. It is true that only a few of the elements — twelve 

 in number — are found in living matter ; these are, 

 especially, carbon, hydrogen, sulphur, nitrogen, and 

 oxygen. But while the elements of organisms are the 

 same as those of the inorganic world, they enter into 

 different compounds in living things from those we find 

 anywhere else. Of these compounds it is especially the 

 albuminoids that distinguish the living substance and are 

 never absent from it. They are very elaborate com- 

 pounds ; we have succeeded in analysing them, but 

 not in building them up from their known elements, 

 because we do not know the arrangement of these, 

 nor the forces and concomitant circumstances in which 

 the elements enter into an albuminous combination — 

 in the way that we found heat uniting sulphur and 

 copper into sulphuret of copper. 



Thus there is no difference in principle between the 

 composition of living and lifeless matter. Nor is there 

 any essential difference between the forces at work in 



