CHAPTER XI. 

 PHYSIOLOGICAL ACTIVITIES (Continued). 



PRODUCTION OF ACIDS. 



The production of organic acids has been sufficiently dis- 

 cussed in preceding chapters. It should be noted that not 

 only these in great variety are produced by bacteria but that 

 under certain conditions mineral acids, such as nitric, sul- 

 phuric and phosphoric may be formed (see Oxidation, p. 102). 

 Acid production is of great value in the identification of 

 bacteria in dairy and soil work and in connection with 

 certain types of pathogenic bacteria. 



GAS PRODUCTION. 



It will be sufficient merely to enumerate collectively the 

 various gases mentioned in preceding paragraphs and to 

 state that those commonly observed in the study of patho- 

 genic bacteria are the first six mentioned. Most of them 

 come in in dairy work either in the study of bacteria causing 

 milk and cheese "failures" or as affecting the flavors of 

 butter or cheese. In the study of soil organisms, any or all 

 of them are liable to be of importance. The gases are: 

 CO2, H, CH4, N, NH3, H2S, gaseous mercaptans, gaseous 

 ptomaines, volatile fatty acids, ethereal salts or esters and 

 others, both of pleasant and of foul odor, but of unknown 

 composition. 



PRODUCTION OF ESTERS. 



The production of esters, as mentioned in Chapters IX 

 and X, of various alcohols and aldehydes are activities 

 which are sometimes of value in the study of bacteria, but 

 need not be further discussed. 



