CHAP. i.J CONSTITUTION OF MATTER. 9 



consequence the organic substance of the gastric juice achieves 

 in these alimentary substances an isomeric 'modification, which 

 renders them liquid, absorbable, in short, transforms them into 

 albuminose. In the same way, under the influence of sulphuric 

 acid diluted, cane-sugar, cellulose, gums, and fecules are metamor- 

 phosed first of all into dextrine, and then into glycose, or grape- 

 sugar. 



These are isomeric catalyses. 



The hippuric acid of the urines of herbivorous animals 

 unfolds itself, under the 'influence of the mucous elements 

 modified by the air, into hippuric acid and sugar of gelatine or 

 glycocoll. 



That is an unfolded catalysis. 



In sum, the universe must be regarded as a whole composed 

 of atoms dissimilar, and variously grouped according to their 

 affinities. These active atoms are the foundation, the substance, 

 the cause of all things : to use the expression of Tyndall, they 

 are giants travestied. 



The various aspects of bodies result from the various modes 

 of aggregation of the constituent elements. 



" All the changes accomplished on the surface of the globe are 

 due to combinations which are made or to combinations which 

 are unmade." l 



All chemical phenomena are consequently the expression of 

 atomic combinations, and can be included in four general 

 types: 



1. Simple change of molecular structure, or isomeria. 



2. Unfolding of compound molecules. 



3. Adjunction, addition of atoms, or of molecules not yet 

 saturated, or, inversely, subtraction of atoms. 



4. Substitution of certain atoms, certain molecules for others 

 in a compound body. 



These general characteristics manifestly exclude all ulti- 

 mate, all radical difference between living organised bodies and 



1 Dumas, Traiti de Chimie, t. viii. 



