MECHANISM OF CHEMICAL CHANGES 169 



present in the medium which have dissolved out from the 

 bacterial cell and which are not present in rapidly growing 

 young cultures. Sometimes these products resulting from 

 autolysis or self-digestion are poisonous in nature. 



3. The Synthetic Action of Enzymes. It will be recalled 

 that not only are enzymes analytic in their action, but they 

 are synthetic as well. Many times complex compounds are 

 produced from simple compounds as a result of bacterial 

 activity. Such, for example, are the gums and the slimes of 

 various species of bacteria. The organism producing ropy 

 milk, for example, polymerizes the sugars present into much 

 more complex gums, usually galactans. The toxins and the 

 enzymes themselves are likewise the result of synthetic 

 action. 



4. Secondary Action of Growth Products. Some of the 

 ultimate products of the action of microorganisms are 

 secondary, that is, products formed within a cell may upon 

 excretion bring about changes in other substances wholly 

 outside of the cell. For example, certain bacteria growing 

 in milk containing calcium carbonate would produce lactic 

 acid, this, upon diffusing from the cell, would form calcium 

 lactate, with the evolution of carbon dioxide. It can scarcely 

 be said that the carbon dioxide is developed as a result of 

 the direct action of the microorganism, but that it is the 

 result of a secondary change. Some of these secondary 

 reactions are of considerable importance in the soil. The 

 insoluble phosphates, for example, are in part at least 

 made soluble and available to the plant roots through the 

 action of secondary products of the growth of bacteria. Not 

 infrequently in fermenting materials gaseous hydrogen is 

 developed. This as nascent hydrogen may exert a powerful 

 reducing action upon various substances present. For 

 example, levulose when fermented by certain bacteria is 

 transformed in part into mannitol, that is, the sugar is 

 changed into the corresponding polyatomic alcohol. 



