6 THE USES AND ORIGIN 



can be selected than the case of mercuric iodide, a sub- 

 stance well known to exist in two totally distinct crystalline 

 forms which differ also in colour. Watts says — " The red 

 crystals turn yellow when heated, and resume their red 

 tint on cooling. The yellow crystals obtained by subli- 

 mation retain their colour when cooled ; but, on the 

 slightest rubbing or stirring with a pointed instrument, 

 the part which is touched turns scarlet, and this change 

 of colour extends with a slight motion, as if the mass were 

 alive, throughout the whole group of crystals as far as 

 they adhere together." 



Thus, it would appear that the phenomena of allo- 

 tropism and dimorphism, and the fluxes from the crys- 

 talloid to the colloid state and the reverse, are strictly 

 comparable with the transformations from the vegetal to 

 the animal, and from the animal to the vegetal, modes of 

 growth so common amongst ' ephemeromorphs.' The 

 members of the animal and the vegetal worlds may be 

 regarded as self-multiplying and progressively varying 

 products, resulting from developments which are con- 

 tinually taking origin from what may be regarded as 

 different allotropic states of Living Matter. 



-y^ * * * * 



Of the organisms appearing as constituents of the 

 ephemeromorphic assemblage of vital forms, x^mcebaB may 

 perhaps be cited as the simplest types of unquestionably 

 animal life; just as some of the smallest Confervae or 

 Moulds are amongst the simplest known forms of the 

 vegetal type or mode of growth. 



ConferviB or Moulds, after the fashion of plants generally, 

 feed upon the inorganic elements existing around them 

 either in water or in air ; Amoebae, after the manner of 

 animals generally, feed upon matter which is either living 

 or which has once lived. This difference between plants 



