Coagulation Types. 



According to Wolff and Weigmann the Bacterium fluorescens 

 possesses the characteristic of producing by itself an ester-like 

 odor, while together with the Bacterium mycoides and the Strep- 

 tococcus lacticus it produces a disagreeable aroma, and finally 

 with the Bacterium megatherium, B. mycoides, and lactic acid 

 bacilli it produces a cheesy odor. This of course renders the study 

 of milk defects difficult, since a bacterium cultivated in pure culture 

 may show an entirey different action than when present in milk in 

 a mixed culture, and mixed culture experiments with the entire 

 flora would become necessary. 



Types of Coagulation. 



The decomposition and fermentation microorganisms, which 

 develop in milk, are utilized in the examination of milk that is in- 

 tended for the manufacture of cheese. A fermentation test is 

 made from each delivery of milk, and after a certain time each 

 sample is tested for odor, taste, and in regard to its appearance 

 and visible changes. 



According to Jensen the fermentation may be distinguished as : 



1. A fluid type, 



2. A jelly type, 



3. A gaseous type, 



4. A whey type, 



5. A cheesy type. 



It should be emphasized that milk samples rich in bacteria 

 usually produce a good jellylike type, whereas in milk samples 

 containing few bacteria, whey fermentation frequently occurs. 



The jelly type results in the profuse presence of lactic acid 

 formers, which distend and tear the coagulum by the action of 

 aerogenes varieties and cheese bacteria, whose gas production fre- 

 quently forces the coagulum upwards. The milk becomes whey 

 when true saccharomyces varieties form gas at the moment of 

 coagulation. At the same time sub-types may be distinguished, 

 such as porous, granular and flaky. The cheesy fermentation 

 type develops in the presence of an increased number of rennet- 

 producing bacteria. 



These fermentation tests of milk are important to ascertain if 

 it is in satisfactory condition for cheese production. For the de- 

 termination of its fitness for drinking purposes, however, these 

 tests are of little importance, since the questions relative to the 

 value which these bacteria possess in the nutrition of man, have 

 never been satisfactorily answered. 



Bacterial Reductase, Bacterial Catalase and Lactic Acid 



Production. 



Among the characteristics of milk bacteria, which are of 

 especial interest are those which are utilized in the examination 

 of milk, and which may have a disturbing effect in experiments 



