2 BACTERIOLOGICAL AND ENZYME CHEMISTEY 



converted into a lime salt by the addition of lime, and the lime 

 salt finally fused with caustic soda, producing the sodium salt 

 of di-hydroxy-anthraquinone or alizarine. 



The artificial preparation of such substances as indigo, 

 camphor and terpenes, uric acid, etc., is even more com- 

 plicated, although the actual chemical reactions may not 

 always be of so drastic a character. 



The same contrast between natural and artificial processes 

 is observable when the change results in the decomposition of 

 substances. Thus to saponify a fat, i.e., to split it up into its 

 constituents, viz., a fatty acid and glycerine, by chemical 

 means, high pressure steam or strong acid or alkali is neces- 

 sary, a condition of things which obviously does not obtain in 

 the ordinary processes of fat digestion in the body. Moreover 

 certain chemical changes which have so far not been artificially 

 produced are brought about with the greatest ease by living 

 matter ; thus, e.g., cellulose, a carbohydrate of the general 

 formula (C 6 H 10 5 ) n can be split up by fermentation into marsh 

 gas, CH 4 , hydrogen, H, and carbon dioxide, C0 2 , and various 

 subsidiary products. This change can be observed in nearly 

 any green stagnant pond, the mud on the bottom of which 

 generally yields copious bubbles of gas if stirred, and one of 

 the famous frescoes by Ford Madox Brown in the Man- 

 chester Town Hall represents John Dalton, Manchester's 

 great chemical philosopher, collecting marsh gas in this way. 



The well-known and extremely important alcoholic fer- 

 mentation of grape sugar is similarly instructive. By the 

 action of yeast this readily yields alcohol and carbon dioxide 

 roughly in accordance with the following equation : 



C 6 H 12 6 = 2C 2 H 5 OH + 2C0 2 



In this case also, simple as the change appears, it has not 

 been hitherto possible to bring it about under strictly artificial 

 conditions. 



In seeking to elucidate the conditions under which these 



