STATE BOAIID OF AGRICULTURE, 



A PRELIMINARY NOTE ON THE ASSOCIATIVE ACTION OF BACTERIA IN 

 THE SOURING OF MILK AND IN OTHER MILK FERMENTATIONS. 



EY CHARLES E. MARSHALL. 



Special Bulletin No. 2.'5. 



While aiming specifically to secure further information concerning the "Al-ration 

 of milk," I isolated two species of micro-organisms from the milk of our college 

 dairy which should be as diametrically opposed to each other as possible: one was 

 a member of the group of lactic acid bacteria and the other belonged to the pep- 

 tonizing class, constantly found in our college dairy milk and producing no acidity. 

 Frequently I have brought two different species together in milk culture and have 

 found an alteration in results which would be secured by either, but up to this 

 time had not thought it worth the effort to combine a species of lactic acid 

 bacteria with one of a class so different. It is not my purpose at this time to 

 ^o into a detailed study of these two species of bacteria from a cultural and 

 biologic standpoint, but rather to state as concisely as possible some of the con- 

 clusive experimental evidence which I have accumulated thus far. I hope to prose- 

 cute this work with vigor until I shall be able to give some idea of its extent and 

 the practical bearing it may have. 



The associative action is appai'ently indifferently understood in the fields of 

 milk, fermentation, and pathogenic bacteriology, although it has been known for a 

 long time that bacterial association is of variable and frequently of great im- 

 portance in the application of bacteriologic knowledge. A pure culture may tell, 

 if conditions are maintained, of the individual and isolated action of a bacterium, 

 but by no means tells its action v/hen brought into the influential company of 

 another species of bacteria, especially if both are cultivated together in their 

 natural environment. Analysis and synthesis should go together hand in hand, 

 otherwise our conclusions might be like studying man apart from society in order 

 to obtain his social relations. 



The customary belief regarding lactic acid fermentation in milk is simple and 

 has been so long established that modifications have not gained way. What we 

 have to offer does not in any manner alter the understanding of the simple nature 

 of fermentation of lactic acid under pure culture, but it has Its bearing by its 

 qualification of lactic acid fermentation in its application where other bacteria 

 are involved. We have always assumed that the lactic acid bacteria would remain 

 uninfluenced by other bacteria in milk or at most would only be retarded in a 

 struggle and would gradually make their way by killing off or inhibiting the growth 

 of other bacteria to the extent of their capacity to produce lactic acid from the 

 lactose. With this working hypothesis, bacteriologists have made much advance, 

 but have been unable to explain many phenomena attending lactic acid fermen- 

 tation in milk other than to attribute them to possible deviations, variations, altera- 

 tions, exaltations of virulence, due to the disturbances of the life per se of the 

 lactic acid bacteria, 



Let us designate our cultures as follows for the sake of brevity: 



A=:Lactic acid bacterium in litmus milk culture. When used as a starter in 

 the dairy it was pronounced by Mr. Michels, the college dairyman, as excellent. 



B^::^Peptonizing bacterium, eventually producing slimy milk. 



A4-B=::Equal amounts of a 24-hour bouillon culture of A and B in the same 

 amount of litmus milk employed in each culture A and B, 100 c. c. in each instance 



There is no test applied which will yield more convincing proof than to watch 

 the cultures closely for a period of several days, for in them may be read the 

 entire history, although not furnishing any intimate knowledge of the changes. 



Making cultures with definite amounts of cultural material used for inocula 

 tion into definite amounts of litmus milk, and placing these flasks at constant 

 temperatures, the results ought to be very apparent, if carefully observed. If it 

 is found later that more specific data are necessary for demonstration, we shall 

 add the details in anticipated future articles on this subject. 



The history of two gross test cultural experiments will perhaps be sufficient to 



