95 



Ammonia, amid nitrogen, lactose, and acidity were estimated in the 

 sterile milk before inoculation for the purpose of comparison. This 

 gave for lactose 4.99 per cent., total niti'ogen .56 per cent., and acidity 

 .17 per cent, as lactic acid. Ammonia .89 per cent, and for amid nitrogen 

 2.87 per cent, based on total nitrogen present in the sterile milk. 



The changes in acidity for the different bacteria are shown in Table 

 IV. 



TABLE IV. 

 Showing changes in acidity, expressed in per cent, of lactic acid, during the period of sixteen days. 



Per Cent. Lactic Acid. 



B. proteus 



B. viscosus 



B. butyricus 



B. mycoides 



B. lactis acidi 



B. mesentericus 



B. liquifaciens . ....... 



B. fluorescens putidus. 



B. subtilis 



B. megatherium 



B. coli 



.027 

 .324 

 .180 

 .261 

 1.161 

 .459 

 .9119 

 .045 

 .468 

 .360 

 .135 



Comparing Tables III and IV, it is shown that the acidity of the 

 milk medium is not in proportion to the loss of lactose, nor gain in 

 ammonia. Therefore neither the production of ammonia nor the acidity 

 is an exclusive measure of the activity of the organisms. It has been 

 stated that the production of ammonia is an index of the metabolic activ- 

 ity of the organisms. This must be taken with some qualification inas- 

 much as proteolysis does not take place by leaps ; that is, that the differ- 

 ent cleavage products are produced in regular order, as proteoses, pep- 

 tids, amino acids, etc., but it is more natural and in harmony with en- 

 zymic action on proteins and carbohydrates, that as soon as proteolysis 

 begins, a series of simpler compounds are formed and all the cleavage 

 products appear, the proportion depending upon the medium, kind of or- 

 ganisms, and enzymes produced by each specific bacterium. Since it is 

 possible to measure the production amino acids and ammonia at short 

 intervals with a good degree of accuracy, it has given additional evidence 

 to show the mode and rate of the activity of bacterial metabolism and 

 their proteolytic power. 



Of the eleven bacteria studied there was a continual change in acid- 



