CONSTITUTION OF LIVING MATTER 63 



ozone which is supposed to be represented by O4. Sulphur 

 crystallises in rhombic octahedrons belonging to the trimetric 

 system, and also in rhombic prisms belonging to the monocUnic 

 system. The latter have a deep yellow colour and are trans- 

 lucent, and always exhibit a great tendency to pass by molecular 

 rearrangement — accompanied by an evolution of heat— into the 

 opaque, straw-yellow, octahedral crystals. 



There are, again, two varieties of phosphorus, known by the 

 name of ' normal ' and ' red Phosphorus.' The first variety is 

 much more poisonous than the second ; it is also colourless, 

 crystallisable in rhomboid dodecahedra, soluble in sulphide of 

 carbon, easily oxidisable, phosphorescent, and inflammable at a 

 low temperature. The second form is chocolate or puce coloured, 

 amorphous, much less soluble, non-phosphorescent, and not in- 

 flammable even at high temperatures. Lemoine has shown that 

 heat is the most available means for converting the one form into 

 the other, and that the transformation is always only partial. 



Arsenic, antimony and other metals, also exist in allotropic 

 states, and the two states of each exhibit wholly different pro- 

 perties. 



These phenomena of allotropism show that even simple bodies 

 — such as carbon, phosphorus, sulphur, and the metallic elements — 

 are made up of molecules composed of similar atoms existing in 

 varying though definite number and grouping in each allotropic 

 state that may exist. An alteration of the number or grouping of 

 the atoms in the molecules, or of both, seems indeed to be the 

 only way of accounting for the wholly different properties and 

 crystalline forms of one and the same substance, such as sulphur, 

 under the influence of different physical conditions. 



Thus vanishes a part of the difference between simple or 

 elementary, and compound bodies. They are all made up of 

 molecules ; only those of the simple substances are aggregates of 

 similar atoms, while those of compound substances are aggregates 

 of dissimilar atoms. 



Different compound substances vary, of course, immensely in 

 their degree of molecular complexity. Some, such as ordinary 

 acids or bases, are aggregates of simply complex molecules ; others 

 are aggregates of doubly complex molecules — that is to say, two 

 simply complex molecules combine to form a doubly complex 

 molecule, and these include, among other compounds, the very 

 common class of bodies known as ' salts.' Seeing that in bodies of 



