I 



THE ROTTING OF WOOD 265 



But if other bacteria which form an enzym called lactase 

 are present, milk sugar will be split, after the addition of 

 a molecule of water, into glucose and another sugar called 

 galactose. This can be converted into alcohol and lactic 

 acid by further bacterial enzym action. Koumiss, kephir, 

 yogurt, etc., are milk derivatives used as drinks by certain 

 races, which are now occasionally prescribed and con- 

 sumed in limited quantities in this country, and which 

 are obtained by the action of bacteria and yeast on the 

 milk of cows, goats, etc. These various products are 

 formed at the same time that a certain amount of energy 

 is released, and as they can be still further oxidized until 

 CO2 and HoO are the end products, still further amounts 

 of energy may be obtained from them. Finally, all the 

 energy used in the manufacture of sugar in the first place 

 will be released, the organisms concerned being duly 

 nourished by the various ingredients of the milk. 



The Rotting of Wood. — The cell-walls of plants con- 

 stitute the bulk of their remains, consisting of cellulose 

 or some derivative of it, as in the wood of trees. Some 

 animals are able to digest these substances by means of 

 enzyms which act upon them and convert them into sugar 

 which they proceed to use in the usual way. Thus, goats 

 can digest cellulose, although we cannot. Bark- and 

 wood-borers digest wood and produce sugar. Fungi are 

 the chief agents in clearing away the remains of plants. 

 Many fungi are able to dissolve their way through wood 

 of both living and dead plants by means of proper enzyms. 

 When fungi attack and thus digest the cell-walls of living 

 plants they cause disease. When the same materials are 

 acted upon by organisms living upon the lifeless remains 

 of these same species, the result is beneficial. The action 

 in both cases is by means of appropriate enzyms. Thus 

 cytase dissolves pure cellulose, while hadromase dissolves 

 wood. The final products in all cases are CO2 and H2O. 



Commercial Fiber Production. — Pectinase dissolves 

 the substance which cements the walls of the fibrous cells 



