CHEMICAL CHANGES WROUGHT BY BACTERIA 37 



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 

 (phosphorescent bacteria on sea water), and many 

 form coloring matter both in nature and when grown 

 artificially (colored mould on preserves). 



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 intestinal intoxication. 1 MetchnikofTs 

 experiments have show r n that the high acid produced by 

 certain saprophytes, the lactic acid germs in particular, 

 is inimical to the producers of this disturbance. In 

 practice, therefore, cultures of these bacteria are 

 administered by mouth. 



1 Auto-intoxication is a term sometimes given to this condition, 

 but it is incorrect and should be limited to disease due to some 

 functional disorder of digestion. 



