PRODUCTS OF METABOLISM. 103 



Perdrix found the relation of hydrogen to carbon dioxide to be at first 

 65:35, later 52:48, and the relation of butyric to acetic acid 26:74, and 

 later 85:15. Perdrix tries to account for this change by assuming three 

 different phases of the process at various ages of the cultures, represented 

 by the following equations: 



First stage: 56C 6 H 12 O a + 42 H 2 O= n6H 2 + n 4 CO 2 + 3oCH 3 COOH+ 



Dextrose Acetic acid 



3 6CH 3 CH 2 CH 2 COOH. 



Butyric acid 



Second stage: 46C 6 H 12 O 6 -f- i8H 2 O= ii2H 2 + 94CO 2 + i5CH 3 COOH+ 



3 8CH 3 CH 2 CH 2 COOH. 

 Third stage: C 6 H 12 O 6 =2H 2 +2CO 2 +CH 3 CH 2 CH 2 COOH. 



It does not seem very probable that the protoplasm of the butyric 

 organism takes up 56 dextrose molecules at once and changes their 

 molecular structures. It is possible that the hydrogen, the carbonic acid, 

 and the organic acids are produced by three or four different processes 

 taking place at once in the same cell independent of each other, and 

 that by certain influences the one is favored, the other checked. But 

 there is no proof for such a theory. 



In fermentations where acid is produced, it will naturally make a very 

 great difference whether this acid is neutralized or not. All organisms are 

 retarded by their own products, and the acid-producing bacteria often 

 give rise to so much acid that it kills them. The neutralization of the 

 free acid will permit them to make more acid. Oxalic acid is produced 

 in large quantities by Aspergillus niger if calcium carbonate is present 

 to neutralize the acid. Without calcium carbonate, only about one-sixth 

 of the amount of acid is produced. In some instances the acidity or 

 alkalinity of the medium may also have a decided influence upon the 

 nature of the products of fermentation. The proportion of acids and 

 alcohols in butyric fermentation is said to be altered materially by the 

 addition of calcium carbonate. 



Other complications occur when an organism is able to use its own 

 products as food, as is the case with some acetic bacteria. They will 

 at first produce considerable amounts of acetic acid and after a while 

 they oxidize the acid completely. It becomes impossible to account for 

 microbial activity by a chemical equation when several organic compounds 

 are decomposed at the same time as is found to occur in some foods, as 

 butter, cheese, ensilage and in sewage. It is also impossible to formulate 



