522 STATE BOARD OF AGRICULTURE. 



EXTENDED STUDIES OF THE ASSOCIATIVE ACTION OF BACTERIA IN 



THE SOURING OF MILK.* 



CHARLES E. MARSHALL. 



[Special Bulletin No. 33.] 



Two articles have already appeared upon this subject, published in the Cent. f. 

 Bakt.- II, Bd. XI, Nos. 24-25, and Bd. XII, Nos. 19-21. The investigations here 

 presented are simply a continuation of the articles named with the purpose of 

 furnishing a more intimate and extended acquaintance with this particular asso- 

 ciative influence of bacteria upon the souring of milk. The studies will embody 

 illustrative experimental data without any attempt to include all results, and 

 will serve the writer's purpose in putting forth his summary without becoming 

 too cumbersome; at the same time it will present the case in sufficient complete- 

 ness for confirmation or further development, should either be. undertaken. The 

 material may be included and discussed under the following sub-topics: 



I. A brief and pertinent historical consideration. 



a. General. 



b. Comments. 



c. Review- of previous personal work. 



II. The significance of different milks and their relation to germ develop- 

 ment. 



III. The changes produced in milk by germ B.j 



IV. The possibilities of acid production In milk during the early stages of 



development of germ B. 

 V. The extent of this associative action in the souring of milk or the in- 

 fluence of other germs than germ B upon germ A. J 

 VI. How the influencing of germ B upon germ A may he demonstrated in 



making butter. 

 VII. History of germ B. 

 VIII. Summary. 



I a. GENERAL. 



Many associative fermentations are familiar to bacteriologists, — on the one 

 extreme one species is known to favor certain well defined changes by its influ- 

 ence upon another species, on the other extreme there are many instances in 

 which decided antagonism is manifested by one species over another, • thereby 

 modifying fermentative results greatly. The extent of these associations with all 

 degrees of possibilities cannot be determined in the present state of our knowl- 

 edge; still there is much evidence which makes this phase of bacteriology not 

 only important in its contributions to an advanced knowledge of the science, but, 

 moreover, in its application to economic problems; Wherever life is found, 

 whether in the form of plants or animals, there may be seen to exist the deter- 

 mining influence of some definite or indefinite association. 



An exhaustive historical review would be out of place in this article because of 

 its possible great extent and of the numerous diversions into other fields it would 

 suggest, all of which would be interesting but not especially pertinent, and w-ould 

 produce a scattering of ideas where concentration is wished. It is more direct 



♦Included with these studies will be a somewjiat prolonged consideration of milk variation in its relation to bacteriological 

 concUisi'ins. 



tOcrm B, the life history of which is given at the end of this article, is the bnctcrinm which is known to esert a favorable 

 influence upon the lactic bacterium studied, throughout this paper, this micro-organism will be designated as germ B or cul- 

 ture B. 



}Genn A or culture A always refers to B. acidi lactici of Weigmann, Thierfelder, Esten, and others. 



