138 Report oF THE BACTERIOLOGIST OF THE 
In order to make the control of the temperature as well as the 
collection of the desired data more accurate the milk was thor- 
oughly mixed in a tempering vat before starting the machine. 
The arrangement of the apparatus will be better understood by 
referring to Plate III. 
DATA COLLECTED. 
In the Dairy the interest centered upon the temperature used 
and in the Laboratory upon the numerical content of germs in 
the milk before and after heating. A large amount of data was 
collected in both places bearing upon a number of points. Notes 
were taken upon the age, weight, initial temperature and acidity 
of the milk, the steam pressure in the boiler, the rate of the 
pasteurization and the maximum, minimum and _ pasteurizing 
temperature employed. 
Age.— With age there is an increased growth of bacteria and 
a larger number of spores present. ‘This is what makes the suc- 
cessful pasteurization of milk over 24 hours old so difficult. 
During a large part of the time the mixted milk was made up of 
portions 4, 12, 24 and 36 hours old. 
Weight.— This varied considerably but averaged 350 lbs. As 
the machine while in operation contained only about five pounds 
of milk and all that was really necessary was to hold the tempera- 
ture at the desired point at the time of taking the sample this 
was quite enough for our purpose. 
Imtial temperature.— The termperature of the mixed milk was 
noted in the tempering vat. For the most part our milk was 
brought to about 26° OC. (78.8° F.) as being a high average tem- 
perature for summer conditions. As received ordinarily in cream- 
eries in this State milk varies from near the freezing point in 
winter to 35° C. (95° F.) in rare cases in summer. 
The temperature of the milk as it enters the pasteurizer exerts 
an influence upon the amount that the machine can heat to a 
desired degree. 
