CATALYSIS AND THE ENZYMES 



of reduction. These so-called Reductases seem 

 to be widely spread in lower and in higher plants. 

 Finally, we have to report that enzymes take 

 part in the formation of such products of meta- 

 bolism as are no longer of any use for the organism. 

 They are removed from it as excretions, or form 

 in the tissue deposits which do not change. In 

 animal life a great quantity of nitrogenous sub- 

 stances are eliminated from the organism, as urea 

 and uric acid. It has been shown by several 

 authors that enzymes participate when these 

 excretion substances are formed. When the 

 bacteria which cause putrefaction of meat are 

 preparing their cell-substances from the proteins, 

 a number of atom-groups from protein are elimin- 

 ated as waste substances. Particularly when 

 putrefaction is going on without sufficient access 

 of air, many substances are formed which are 

 responsible for the peculiar smell of putrid matter, 

 and which are to be considered as bacterial excre- 

 tions. Such are some compounds of sulphur, 

 hydrogen sulphide itself, and methyl-mercaptan ; 

 further, indol and scatol are substances which are 

 very characteristic of putridity. No less must a 

 series of phenols be mentioned as products of 

 putrefaction. We have certain proofs for the view 

 that all these substances take their origin from 

 amino-acids, which are the primary products of 

 the decomposition of proteids. By splitting of 

 carbon dioxide and of ammonia the formation of 



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