FOEMS OF BACTERIA 17 



list may be considerably extended. In this way a large number of 

 acids (e.g. butyric, lactic, acetic), esters, and alcohols, have been 

 identified; also methane, carbon dioxide, hydrogen, sulphuretted 

 hydrogen, ammonia compounds, nitrous- and nitric-compounds, free 

 nitrogen, and many others. Some are extruded from the cell in the 

 form of gas, others are extruded in the liquid or solid condition, 

 whilst a third group is retained in the cell, chiefly in the vacuoles. 

 A complete list of all the substances that are found inside the cells of 

 bacteria would probably include a very large percentage of all the 

 organic compounds known to chemists. 



