150 ATLAS OF BACTERIOLOGY. 



always find, at least in traces, formic acid, acetic 

 acid, proprionic acid, butyric acid, and not infre- 

 quently some ethyl alcohol, aldehyde, or acetone. In 

 rarer cases the lactic acid is wanting and only the 

 other acids are formed. 



In order to obtain and separate the acids we 

 employ the following method : In 1 litre flasks are 

 placed i litre peptone bouillon with two to five per 

 cent grape sugar or milk sugar and perhaps 

 10 gm. calcium carbonate. The acids formed com- 

 bine with the calcium carbonate into a soluble 

 lime salt and carbonic acid escapes; the reaction 

 of the fluid and that is the main thing remains 

 neutral. A strongly acid reaction would inter- 

 fere prematurely with the farther growth of the 

 bacteria. 



When the growth has ceased (in eight to fourteen 

 days) the undissolved carbonate is filtered off, and 

 the reaction being neutral, the alcohol, aldehyde, 

 acetone, etc. , are distilled ; the fluid is boiled down 

 considerably during this process. The three sub- 

 stances just mentioned are detected in common by 

 Lieben's iodoform reaction. To the slightly warmed 

 fluid in a test tube are added five to six drops of 

 pure ten-per-cent potash lye, then a weak iodine- 

 potassium iodide solution is added drop by drop 

 until a brown color is produced, and the latter is 

 made to disappear by a drop of potash. The charac- 

 teristic iodoform odor and the precipitation of micro- 

 scopic small six-angled iodoform plates are convinc- 

 ing evidence. For the differentiation of alcohol, 

 aldehyde, and acetone, vide Yortmann, " Analyse or- 

 gan. Stoffe," 1891. 



