74 INTEODUCTION. 



of different chemists have shown that proteine itself has an 

 indefinite chemical composition, hardly any two formulae 

 being the same. It is essentially an artificial product ; and 

 with the views we have taken .of the composition of organic 

 substances, there is not the slightest reason to suppose that 

 it plays the part of a base or radical for a group of definite 

 compounds. It is not a distinct chemical substance, for 

 its composition is indefinite ; nor a proximate principle, for it 

 is produced artificially and by decomposition. We must 

 therefore reject the theory that it serves as the radical of a 

 definite series, and discard the name of Proteine Compounds, 

 as applied to organic principles. 



Catalysis. Catalysis, or catalytic action, is a name given 

 to a certain process which we do not as yet understand. The 

 word was introduced by Berzelius in 1835, and applied to 

 certain actions or affinities brought into play in inorganic 

 bodies by the mere presence of another substance, the latter 

 not undergoing any chemical alteration. It is now applied 

 to all chemical changes which are induced by the simple 

 presence of any substance, like the particular class of sub- 

 stances called ferments, in which the substance inducing this 

 action undergoes no chemical change. Fermentation, which 

 was considered in treating of sugar, is an example of catalysis ; 

 the sugar being decomposed into carbonic acid and alcohol from 

 the fact of the mere presence of yeast, which has nothing to 

 do, chemically, with the process. Putrefaction, which we 

 have just considered, is an example of catalysis ; for a small 

 quantity of any animal substance in a state of putrefaction 

 is capable, by its presence, of setting up the same process in 

 other principles of this class. Nutrition, and to a certain ex- 

 tent digestion, are examples of catalysis ; for in the repair 

 of the system, certain materials are taken from the blood by 

 the tissues, and by the latter changed into different sub- 

 stances, as musculine for the muscles, osteine for the bones, 

 etc. ; and in digestion, the organic elements which are dissolved 



