EXPERIMENT STATION BULLETINS. 557 



FOREWORD. 



Milk is a most highly decomposable food. Ranking as it does at the top 

 of the list of foods from the standpoint of completeness, availability and 

 general acceptability, it tends to occupy the position at the foot of the list 

 from the standpoint of keeping qualities. It is, therefore, very essential 

 that careful study be made not only to devise methods for improving the 

 quality and prolonging the keeping quality of milk, but also to devise tests 

 whereby the quality and the keeping quality may be easily and accurately 

 estimated. Quite naturally the earliest efforts to determine these points 

 scientifically consisted in using the common bacteriological technique of 

 estimating numbers of bacteria by plating. INIore recent technique has 

 been developed whereby the number of bacteria may be estimated by direct 

 microscopic examination of the milk. Methods are available whereby the 

 amount of dirt in milk may be made visible and estimated. Other tests 

 have resulted from approaching the problem from a different angle, one in 

 particular being based upon the determination of the activity of certain 

 enzymes in the milk. Cooledge and Wyant of this Station have already 

 announced the discovery of a method intended to determine the activity 

 of both bacteria and the enzymes in the milk. This method appears to be 

 both simple and accurate, particularly when the apparatus designed by the 

 former is employed to make the readings. The present bulletin describes 

 the technique employed and the apparatus devised and a comparison of 

 several of the methods that are at present advocated for testing the keeping 

 qualities of milk. There is also included a plan for grading milk and paying 

 9, bonus based on the keeping quality as determined by this method. The 

 method described and employed proves to check far more closely with the 

 actual keeping qualities of the milk than do the other methods with which 

 it is compared. 



The author acknowledges his indebtedness to G. G. Speeker and L. C. 

 Emmons of the Mathematics Department for their assistance in furnishing 

 a mathematical interpretation of Table 7. 



WARD GILTNER. 



