28 STATE BOARD OF AGRICULTURE. 



present shall be centered upon a sinjjle theme which heretofore has 

 not been emphasized and has not even been understood. 



We have always worked with the impression that milk soured from 

 the multiplication of lactrc acid bacteria, and that these bacteria through 

 the vigor of their growth supplanted all other germs present. Further, 

 these lactic acid germs we have understood to overcome all of the 

 possible changes and damages that might occur from the other germs 

 which are present or are associated with them in the milk. What 

 I have to say in regard to this assumption is not in any way going 

 to conflict with our intimate understanding of the souring of milk, — 

 this process takes place from the action of the lactic acid bacteria 

 upon the sugar of the milk, producing lactic acid and sometimes 

 carbonic acid gas. This is simple lactic fermentation. By the for- 

 mation of the acid the casein of the milk is curded, thus we have lop- 

 pered milk. But it is erroneous to think for a minute that the other 

 micro-organisms present in the milk have no influence upon this lactic 

 acid fermentation. Here is where we have erred, for we are able 

 to demonstrate beyond a doubt that where certain germs, diametrically 

 opposite in their nature to the lactic acid bacteria, when associated 

 with them are in some instances able to hasten the souring of the 

 milk bj ninety-six hours, and in other cases they retard the souring 

 of the milk, thus making the process slower. If we were to work under 

 the old assumption we would conclude that the lactic acid bacteria 

 would eventually take care of any damage done by these associated 

 bacteria; this is false. Through the association the results are quite 

 different; in one in the rapidity of souring, in the other in the amount 

 of acid produced, and also in others in the flavor and aroma of the 

 milk. From the work we have done, it follows that a pure milk supply 

 is essential if our starter consisting of lactic acid bacteria is going 

 to perform its best work; because, if you simply add a starter to 

 cream or milk containing these other bacteria, you will partly cor- 

 rect the mischief done but it will be of a very imperfect correction. 

 Again, one might assume that by pasteurizing and killing most of the 

 germs present and then using a starter a complete remedy would 

 be furnished.- This is also false because T find that even after pasteur- 

 izing the products produced by the germs associated with lactic acid 

 bacteria are sufficiently stable to remain in the milk. While pasteur- 

 ization is corrective, it is by no means as good as pure milk. Still, 

 again in the manipulation of the starter it has its bearing because 

 the starter is usually continued in pasteurized milk only. Doubtless 

 the starter many times may remain intact and free from contam- 

 inating influence yet there is always that possibility of associative ac- 

 tion from other germs which will lead to a destruction of the value 

 of the starter. I am informed by Mr. Michels that after he has kept 

 his starter for some time in the usual method employed in a i)rogres- 

 sive dairy he finds that it becomes too sour for satisfactory work 

 and does not possess the value it formerly did. It is probable that 

 such changes are induced by the development of these associative 

 germs. In my own work I have been able to demonstrate, that as 

 the lactic acid bacteria were influenced in their development by certain 

 associative germs, the acidity of the culture could materially increase. 

 I believe also that I can demonstrate that where we have associated 



