igo ECONOMIC BACTERIA IN MILK AND MILK PRODUCTS 



It is clear that in these last three experiments the cream was 

 much fresher than in the creamery experiments, and the results 

 are therefore different. This led to a series of experiments (nine 

 in all) to show the variations in the proportions of the different 

 types of bacteria during cream ripening. One fair example of the 

 results is given, as follows : — 



The various points to which we have made reference are here 

 illustrated in tabular form. The parallel between the rise and fall 

 of the acid organisms in cream and those in our own experiments 

 in milk {see p. 130) is very striking. The rise at forty-eight 

 hours, the prodigious number of organisms then present, and the 

 fact that this is the exact period of the zenith of the lactic acid 

 organisms is shown with remarkable clearness in this Table, and 

 a careful study of it will furnish an exact appreciation of what the 

 ripening process consists. The changes occurring in cream as it 

 ripens are, therefore, due to the enormous multiplication of 

 bacteria, which, by their growth and products, profoundly modify 

 the cream. This multiplication occurs in two stages, the first due 

 to the development of miscellaneous and peptonising species, the 

 second due to the lactic acid species. 



TJie source of lactic organisms. — The origin of the lactic acid 

 organisms in milk and cream is not known. We have carried out 

 various experiments which show — (i) that these organisms do not 

 come from the udder of the cow ; and (2) that these organisms are 

 present in the dust, or air, or surroundings of the byre. Rollin 

 Burr also has carried out experiments with the same object and with 

 much the same results.^ He assumes that the three organisms 



1 Thirteenth Annual Report of Starr's Agricultural Expt. Sta., Connecticut, 

 1900, pp. 66-81 ; also Centralb.f. Bakt., 2nd Abth., 1902, p. 236. 



