EXPERIMENT STATION BULLiETINS. 381 



Class A. Under this class 5 prizes were awarded to farmers 

 delivering milk having the highest average pH score 

 during the contest. 



Class B. Under this class 5 prizes were awarded to farmers 

 delivering millc showing the greatest improvement 

 during the contest. 



Under Class A it was expected to award prizes to those who were de- 

 livering a superior grade of mill<;. Class B was designed to stimulate the 

 interest of patrons whose milk made the poorest showing during the 

 preliminary period. 



THE CONTEST WAS DIVIDED INTO TWO PERIODS. 



Preliminary jjeriod. During this time the samples were taken, in so far 

 as poissible, without the knowledge of the farmers. This period lasted 

 four weeks and represented the. condition of tlie milk as it was delivered 

 before the patrons had knowledge of the contest. It was used as a baisis 

 for judging imiprovement during the contest. 



Contest proper. Immediately after the preliminary period, the patrons 

 were notified of the contest, told of their average score during tlie pre- 

 liminary period and advised as to methods which, if put into practice, 

 might be expected to bring about improvement in the supply. Letters of 

 encouragement and advice were sent to patrons once a week during the 

 contest. These letters told the patrons his average score for the week, and 

 the average score of all the patrons. One week elapsed between the close 

 of the preliminary period and the contest proper. 



EXAMINATION OP SAMPLES. 



The samples taken during the preliminary period and during the contest 

 proper were examined (1) by the pH method, (2) the bacteriological 

 count, (3) the Weinzirl spore test, and (4) for temperature. Experi- 

 mental cheeses were also made from the milk delivered in this contest. 



(1)THE pH METHOD AND ITS DETERMINATION. 



Preparation of Media. The only medium necessary for this work is 

 bouillon cube broth recommended by Wyant (4) containing the indicator. 

 Dibrom thymol sulphonephthalein (Brom-thymol blue). This is made as 

 follows One bouillon cube, 1 percent Witte's or other peptone, and 0.5 

 percent salt are added to each liter of water, this is boiled several minutes 

 and then filtered. 80 cc. of a 0.04 of one percent aqueous solution of brom- 

 thymol blue is then added for each liter of broth. The broth is then 

 cooled to 20 °C. and the color adjusted to compare with tube 6.8 of the 

 standairds which are mentioned later. A compensating blank, broith with- 

 out indicator, must be placed in front of the standard and the readings 

 must be made at room temperature. 



The broth is then placed in 100 or 20O cc. flasks, sterilized, and stored. 

 When needed lOcc. of the broth indicator solution is transferred to a 

 2.8 X 16 cm. sterile test tube with a 10 cc. sterile pipette and compared 

 with standard tube pH 7.0 in the comparator. A few drops of N/1 NaOH 

 or HCl are then added to the flask of indicator solution if needed to 



