EXPERIMENT STATION BULLETINS. 



527 



tion of increased acidity, it must be considered during tlie very early hours of 

 the culture, for soon the alkalinity increases. The formation of a lab enzyme 

 in sufficient quantities after several hours to curdle the milk seems more prob- 

 able, yet even this explanation is by no means final, for this hypothesis and the 

 facts do not coincide as fully as they ought. The cultures in milk show con- 

 siderable advancement in digestion before loppering takes place. It is true that 

 lab enzymes not infrequently form in the presence of peptic digestion, but 

 are unable to manifest themselves on account of the rapid dissolution of the 

 milk. To this it may be said that in some milk cultures curding takes place 

 slightly but perceptibly before much digestion has taken place, while in other 

 milks there is no evidence of curding. In the heating of the cultures, too, the 

 rapid rise of temperature would possibly destroy the enzyme. Of course there 

 is a chance of enzymic action before the temperature becomes too high, yet 

 so far as we can determine, the precipitation does not occur with the warming, 

 but rather with the prolonged heating. To further eludicate this matter in 

 hand, boiled sweet milk can be made to curdle in much the same manner as 

 the flask cultures by the addition of some of a digested milk culture of B of 

 long standing, w'hich has been boiled and filtered. This simple test confirms 

 tvhat Jias been suspected: The products, stable and not enzymic in nature, are 

 able to produce a precipitation. This has been demonstrated with cultures 

 neutral in reaction to litmus and also decidedly alkaline to the same indicator. 

 Neitlier acids nor enzymes but products of another nature apparently cause the 

 curding upon heating. Perhaps we may later be able to show that different 

 milks respond differently to the development of germ life because such products 

 are formed more easily in some milks than others. The differences, therefore, 

 manifested in the above table may be said to be due to the differences in the 

 amount of products manufactured by germ B in the different lots of milk, and 

 further, the measure of the products would also measure the germ development 

 which seemingly has some relation to the character or condition of the milk 

 In which they are grown. 



Another effort to ascertain the variability of different milks, employing germ 

 A, will add to the evidence. In this instance, the time of curding and the meas- 

 ured acidity will serve as the key to the situation. 



Lot of milk (dairy milk.) 



Original acidity 



Number of germs introduced per c cm 



Time of testing acidity of culture 



Acidity of culture 



Time of natural curding 



Temperature maintained, C , 



Five. 



14° 

 692 



120 hrs. 

 27° 



275 hrs. 

 20° 



The lots of milk employed in this test were secured from the dairy on differ- 

 ent days, were inoculated with the same number of germs, were manipulated 

 in the same manner, were maintained at the same temperature, and all the 

 conditions were identical with the exception of the different lots of milk. The 

 results, as indicated by the time of curding and the degree of acidity, are 

 indeed irregular. In the employment of the same lot. of milk, a constancy and 

 uniformity are 'very striking whenever the manipulative processes have been 

 carefully executed. When beginning this work on association, this irregularity 

 growing out of the employment of different lots of milk caused much confusion; 

 fortune favored by requiring the same lot of milk in each test as well as abso- 

 lute uniformity in sterilizing and all other operations in its preparation. It is 

 absolutely necessary to observe accuracy and uniform manipulation, otherwise 

 the operator is likely to fail in associative studies. This may be illustrated by 

 the use of a single lot of milk subjected to uniform treatment for studying 

 cultural results. 



