538 STATE BOARD OF AGRICULTURE. 



the investigator's experience scarcely observable. As the culture ages, the 

 deep orange yellow appears as is the custom with cfther media. 



Milk Culture — The first noticeable change in milk is a very thin yellowish layer 

 of digested milk. This occurs rapidly at 20° C. if the milk is inoculated 

 with large amounts of culture, and even with minute quantities rapid 

 changes may be instituted. The peptonization of milk advances from the sur- 

 face downward, causing so far as can be determined at the start, no alteration 

 of the acidity, but, as the culture ages, there is a very decided falling off in 

 acidity to phenol-phthalein, with a corresponding increase of alkalinity. Not 

 infrequently a perceptible curding of the milk at the bottom of the flask or 

 tube has been found and for some time it was thought that it was due to 

 contamination. With careful manipulation, the conclusion has been reached 

 that the curding seems a property of some milks though perhaps some pro- 

 ducts already formed, in other milks through some inherent characteristic 

 or in still others through a possible contamination. The author has secured 

 this curding in milks, sterilized within an hour from the cow, in fresh dairy 

 milk, in old dairy milk, and always in milk cultures upon heating, — the 

 age of the culture being the determinative factor. As the milk culture ages, 

 a slimy condition manifests itself and remains permanent thereafter. The 

 odor produced in milk begins with that of cheese, passes into that of the 

 pine-apple, and from this to one which touches on putrefaction. The orange 

 yellow pigment is very pronounced in old milk cultures. For a more ex- 

 tended consideration of milk cultures, a study of the body of this article 

 should be made. 



Oxygen Requirements — It falls little short of being an obligate aerobe. Hydrogen 

 greatly retards development. 



Saccharose Bouillon — Acidity reduced from 15" to 6° in 10 days at 20°. 



Glucose Bouillon — Acidity reduced from 15° to 10° in 10 days at 20°. 



Lactose Bouillon — Acidity reduced from 15° to 8° in 10 days at 20°. 



Levulose Bouillon — Acidity reduced from 15° to 14° in 10 days at 20°. 



Starch (soluble) Bouillon — Acidity unchanged. Starch reduced to some form of 

 dextrin. No reducing sugar formed. 



Reaction — Production of alkaline substances in nitrogen degradation from proteid 

 substances. Amido and ammonia compounds found in cultures. 



Gas Production — No gas of any sort ever discovered. 



Indol Reaction — Slightly perceptible in 48 hours. 



'SUMMABY. 



1. Associative or mixed cultures become significant through the development 

 of two or more micro-organisms together in a single series of microbial changes. 



2. Associative or mixed natural cultures are not uncommon and have been 

 known for many years in connection with various well known fermentations 

 and disease processes. 



3. Studies In which it has been shown that lactic bacteria have been favorably 

 influenced in their growth by other bacteria are not known to the investigator. 



4. Lactic bacteria are favorably influenced in their development by the pres- 

 ence of certain other bacteria. 



5. Indications make this possible influence quite extensive. 



G. Products manufactured by these bacteria in milk are known to exert the 

 same influence as the living bacteria. 



7. These products are stable through prolonged sterilization. 



8. It is necessary, in order to demonstrate this associative action satisfac- 

 torily, to note the responses of variable milks from different cows to germ growth, 

 otherwise irregular results will be obtained. 



9. The products of germ B in its gi'owth upon milk suggest many possibilities 

 but no conclusions may be drawn. 



10. The influence exerted in germ B in the making of butter and the amount 

 of starter necessary to bury it, indicates the importance of associative influence 

 in practical dairying. This same influence doubtless extends to cheese. Further, 

 when it is recalled that the products of the germ are stable, it is easily seen 

 how pasteurization or sterilization at times become ineffective in the prepara- 

 tion of milk for consumption or infant feeding and how easily toxic products 



