34 GENERAL BIOLOGY 



state, so that the power of breaking up the material on which 

 they are existing into the elements necessary for the life of 

 the cell has to be done by some process of cellular activity. 

 To do this, bacteria form what are called enzymes or ferments. 

 An enzyme or ferment is a product capable of changing a 

 chemical combination without itself entering into the prod- 

 uct of this change. The bacterial enzymes are comparable 

 to the enzymes found in the digestive juices of the human 

 alimentary canal. There are many kinds of ferments, each 

 having the power of breaking up certain chemical substances. 

 There are ferments splitting up sugars and starches and fats 

 and proteids, and the result of this splitting is simpler in 

 composition than the substance split, thus making it easier of 

 use as food. The ferment activity of bacteria is just like 

 that of yeasts which are used in the industries, especially 

 that of spirituous liquor- making. In this case the organisms 

 and their enzymes are capable of splitting sugar with the 

 production of ethyl alcohol, and specific species or strains 

 are kept by vineyards, distilleries, and breweries for the 

 peculiar kind of fermentation desired. 



Some bacteria have the property of producing light (phos- 

 phorescent bacteria on sea water), and many form coloring 

 matter both in nature and when grown artificially (colored 

 mould on preserves). 



Some of these saprophytes living in the intestine have the 

 power of destroying certain pathogens that gain entrance. 

 Metchnikoff found that certain bacteria produced so much 

 acid, chiefly lactic acid, that many other bacteria could not 

 live in their presence. He took advantage of this to assist 

 in the treatment of certain cases of putrefaction in the 

 intestinal tract. It happens that some intestinal bacteria, 

 perhaps under the stimulation of irregularity of function, 

 may produce too much fermentation of sugars and starches 

 or too great breaking down of the most important food- 

 stuffs, the proteids. From this improper breaking down and 

 absorption of its products comes the so-called intestinal 



