New Yoek Agricttltueal Expeeiment Station. 141 



only acted as an insulator between the milk and the source of heat, 

 but also encroached upon the inten^al between the revolving stirrer 

 paddles and the wall, forming a rough surface along which the 

 milk must pass. The fact that the machine was not permanently 

 placed and lacked in rigidity was also a contributing factor to the 

 above variations. 



Pasteurizing temperature. — As soon as the milk enters the bot- 

 tom of the machine it takes up heat from the steam jacket and 

 its temperature rises to the highest point just as it reaches the 

 milk outlet. The teniperatui'e at this point is measured by a 

 thermometer inserted in the outlet and constitutes the so-called 

 " Pasteurizing Temperature," although the milk really attained 

 this degree only momentarily. As soon as the milk passes from 

 the machine the temperature falls with a rapidity depending upon 

 the surroundings. 



TAKING SAMPLES. 



The samples of unpasteurized milk were taken from the tem- 

 pering vat after the milk had been thoroughly mixed. The only 

 exception to this was during the earlier part of the work, when 

 they were taken from the supply tank just before taking the 

 samples of pasteurized milk from the machine. 



The samples of pasteurized milk were taken from the milk 

 outlet after sufficient had passed to remove the effect of the bac- 

 teria contained in the water used in starting the machine and in 

 the machine itself. Care was taken to secure samples while the 

 machine was running steadily at the desired temperature. 



The samples of about 150 cubic centimeters each in sterile 

 flasks were set into a room at 1.5° to 4.5° C (35°-40° F.) until 

 the pasteurization was ended, when they were taken to the labora- 

 tory on the floor above and the quantitative analyses made. 



BACTERIOLOGICAL TESTS. 



Method of dilution, — One c. e. of the unheated milk was added 

 to 9 c. c. of sterile water and the two thoroughly mixed. This 



