304 STATE BOARD OF AGRICULTURE. 



to make a micro-organism, now without associate influence, possess some 

 associate influence and vice versa. A few degrees of temperature may 

 alter completely the entire development of a micro-organism. 



The variation in the numl^ers of micro-organisms introduced in combi- 

 nation must also produce different results. This is not entirely within the 

 control of the operator, hence causes much annoyance. 



Other factors creep into this work and should be considered; yet with a 

 constant temperature, constant milk, constant controls or checks, all con- 

 ditions the same in every test, the results offer average comparative ma- 

 terial. 



The facts available even with present technique, are very valuable and 

 throw much light upon the suggestive hidden mysteries of the natural lac- 

 tic fermentation of milk. Although our present methods and technique 

 making accuracy unattainable, are to be deprecated, still the results fortify 

 our steps of progress. No doubt, what has been heretofore regarded to a 

 greater or less extent as the simple, natural fermentation of milk, is in its 

 associations a most highly complex fermentation. It is only the heavy 

 burden of our ignorance that makes us consider it in the light of a simple 

 problem. 



In addition to the knowledge acquired by the study of the rise and fall 

 of the different micro-organisms in a sample of milk, the plates made of 

 each sample from time to time materially assisted in the isolation of the 

 various species in pure culture. 



All the care exercised on the start in the study of the samples of milk, 

 as secured from the dairy, was designed primarily for use in the interpre- 

 tation of pure and associate cultures, as well as to measure against the de- 

 tailed results of combinations. The authors anticipated the importance of 

 comparing the souring of a sample in its natural condition with the results 

 which may follow from the study of the association of the various micro- 

 organisms with the lactic micro-organisms. 



As soon as the micro-organisms of a sample were isolated in pure cultures 

 their life histories were carefully studied to the point where the identity of 

 each was well established, making it impossible to duplicate results or dup- 

 licate associate micro-organisms. In these studies, morphological and 

 cultural, no effort was spared to follow out identifying or differentiating 

 features to satisfaction. When this was done the morphological and cul- 

 tural studies of the micro-organisms ceased. No attempt was made to carry 

 the work to identification of species, inasmuch as it was not regarded as 

 especially pertinent to the theme. 



Great attention was given to the isolation of the lactic micro-organism 

 of the sample and the ascertaining of its relation to the souring of the milk. 

 As will be seen later in the detailed records, this was not a difficult task 

 because of the predominance of the lactic micro-organisms toward the end 

 of the fermentation. It was, however, very important that the lactic micro- 

 organism should be secured in pure culture and should be maintained in a 

 vigorous form, because of its central position as a biological factor. To 

 accomplish this, cultures of the lactic micro-organism were kept in milk and 

 transfers frequently made. 



Whenever it was desired to follow out in detail the associate studies, 

 cultures in bouillon of such germs concerned were made and held for twenty- 

 four hours. These twenty-four hour cultures usually gave very vigorous germs 

 for transplanting. From these twenty-four hour cultures dilutions were made 

 -n seven-tenths of one per cent salt solution. The extent of these dilutions 



