CHEMICAL CHANGES WROUGHT BY BACTERIA 35 



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. Advantage is taken of these bacterial ferments 

 in the industries, especially that of spirituous liquor- 

 making. In this case the bacteria 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, 

 and many form coloring matter both in nature and 

 when grown artificially. 



The effect of saprophytes upon pathogenic bacteria 

 in the intestine is that they sometimes destroy the 

 latter. Metchnikoff found that certain bacteria pro- 

 duced 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. 

 Bacteria also may produce various simpler products in 

 the course of their enzyme action. Now it happens 

 that some of the bacteria in the intestinal tract, per- 

 haps 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 foodstuff, the proteids. From this improper 

 breaking down and absorption of its products comes 

 the so-called auto-intoxication. Metchnikoff 's experi- 

 ments have shown that the high acid produced by 



